Laminated film and display device including same

ABSTRACT

Disclosed are a laminated film including a light transmitting substrate; a hard coating layer; and an optical enhancement layer disposed between the light transmitting substrate and the hard coating layer or at a position facing the hard coating layer with the light transmitting substrate therebetween, wherein the light transmitting substrate includes a polyimide, a poly(amide-imide) copolymer, or a combination thereof, and the optical enhancement layer includes a copolymer comprising a polyimide, and a display device including the laminated film.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2018-0120054 filed in the Korean IntellectualProperty Office on Oct. 8, 2018, and all the benefits accruing therefromunder 35 U.S.C. § 119, the content of which in its entirety is hereinincorporated by reference.

BACKGROUND 1. Field

A laminated film and a display device including the laminated film aredisclosed.

2. Description of the Related Art

Portable display devices such as a smart phone or a tablet PC have beenactively researched according to the high performance and popularizationthereof. For example, lightweight, flexible (i.e., bendable or foldable)and portable display devices have been studied and developed to becommercialized. The portable display device of a liquid crystal displayor the like includes a protective window for protecting a display modulesuch as a liquid crystal layer. Currently, most portable display devicesinclude a window including a rigid glass substrate. However, glass isfragile and is easily broken by the exterior impact, when applied to aportable display device or the like, and also glass is not flexible, soit may be not suitable for a flexible display device. Therefore, it hasbeen attempted to substitute a protective window with a plastic film ina display device.

However, the plastic film is needed to further improve mechanicalproperties such as hardness and optical properties in order to beapplied for the protective window in a display device and simultaneouslyto have high appearance quality.

SUMMARY

An embodiment provides a laminated film in which interfacial reflectionsand generation of interference fringes are suppressed to improve opticalcharacteristics and visibility.

Another embodiment provides a display device including a laminated filmhaving improved optical characteristics and visibility.

An embodiment provides a laminated film including a light transmittingsubstrate; a hard coating layer; and an optical enhancement layerdisposed between the light transmitting substrate and the hard coatinglayer or at a position facing the hard coating layer with the lighttransmitting substrate therebetween, wherein the light transmittingsubstrate includes a polyimide, a poly(amide-imide) copolymer, or acombination thereof, and the optical enhancement layer includes acopolymer including a polyimide.

A refractive index of the optical enhancement layer may have a valuebetween a refractive index of the light transmitting substrate and arefractive index of the hard coating layer.

The optical enhancement layer may have a refractive index of about 1.5to about 1.7.

The copolymer including a polyimide of the optical enhancement layer mayinclude (a) an imide structural unit, and (b) a urethane structuralunit, a siloxane structural unit, an amide structural unit, or acombination thereof.

The imide structural unit may be represented by Chemical Formula 1:

In Chemical Formula 1,

D is a substituted or unsubstituted quadrivalent C4 to C30 alicyclicorganic group, a substituted or unsubstituted quadrivalent C6 to C30aromatic organic group, a substituted or unsubstituted quadrivalent C4to C30 heteroaromatic organic group, or a combination thereof, and

the alicyclic organic group, the aromatic organic group, theheteroaromatic organic group, or the combination thereof is a singlering, a condensed ring in which at least two rings are fused, or a ringsystem including at least two rings of the single ring and the condensedring, which are linked by a single bond, a fluorenylene group, —O—, —S—,—C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—,—C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.

The urethane structural unit may be represented by Chemical Formula 2:

*—(—Y—NH—CO—O—Z—)—*   (Chemical Formula 2)

In Chemical Formula 2,

Y and Z are each independently a substituted or unsubstituted divalentC1 to C30 aliphatic organic group, a substituted or unsubstituteddivalent C3 to C30 alicyclic organic group, a substituted orunsubstituted C6 to C30 aromatic organic group, a substituted orunsubstituted C2 to C30 heteroaromatic organic group, or a combinationthereof, and

the alicyclic organic group, the aromatic organic group, theheteroaromatic organic group, or the combination thereof may be a singlering, a condensed ring in which at least two rings are fused, or a ringsystem including at least two rings of the single ring and the condensedring, which are linked by a single bond, a fluorenylene group, —O—, —S—,—C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—,—C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₅H₅)—, —C(═O)NH—, or a combination thereof.

The siloxane structural unit may be represented by Chemical Formula 3:

In Chemical Formula 3,

R^(a) to R^(f) are each independently a substituted or unsubstituted C1to C30 alkyl group, a substituted or unsubstituted C2 to C30 alkenylgroup, a substituted or unsubstituted C2 to C30 alkynyl group, asubstituted or unsubstituted C1 to C30 alkoxy group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC6 to C30 aryl group, an epoxy group-containing group, or a combinationthereof,

L¹ and L² are each independently a single bond, —O—, a substituted orunsubstituted C1 to C30 alkylene group, a substituted or unsubstitutedC1 to C30 heteroalkylene group, a substituted or unsubstituted C2 to C30alkenylene group, a substituted or unsubstituted C3 to C30 cycloalkylenegroup, a substituted or unsubstituted C2 to C30 heterocycloalkylenegroup, a substituted or unsubstituted C6 to C30 aryl group, asubstituted or unsubstituted C2 to C30 heteroaryl group, or acombination thereof, and

m is an integer from 0 to 150.

The amide structural unit may be represented by Chemical Formula 4:

In Chemical Formula 4,

A, E¹, and E² are each independently a substituted or unsubstituteddivalent C1 to C30 aliphatic organic group, a substituted orunsubstituted divalent C3 to C30 alicyclic organic group, a substitutedor unsubstituted divalent C6 to C30 aromatic organic group, asubstituted or unsubstituted divalent C2 to C30 heteroaromatic organicgroup, or a combination thereof, and

the alicyclic organic group, aromatic organic group, heteroaromaticorganic group, or the combination thereof is a single ring, a condensedring in which at least two rings are fused, or a ring system includingat least two rings of the single ring and the condensed ring, which arelinked by a single bond, a fluorenylene group, —O—, —S—, —C(═O)—,—CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—,—C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.

The optical enhancement layer may further include partially condensed(incompletely condensed) polyhedral oligomer silsesquioxane (POSS)including a functional group capable of forming a hydrogen bond at thebroken site of at least one —Si—O—Si— bond.

The partially condensed polyhedral oligomer silsesquioxane including afunctional group capable of forming a hydrogen bond at the broken siteof at least one —Si—O—Si— bond may be represented by Chemical Formula 5or Chemical Formula 6:

In Chemical Formula 5 and Chemical Formula 6,

R is each independently a substituted or unsubstituted C1 to C30 alkylgroup, a substituted or unsubstituted C3 to C30 cycloalkyl group, asubstituted or unsubstituted C6 to C30 aryl group, or a combinationthereof, and

R′ is each independently —OH, —SH, or —NH₂.

The partially condensed polyhedral oligomer silsesquioxane including afunctional group capable of forming a hydrogen bond at the broken siteof at least one —Si—O—Si— bond may be included in an amount of less thanor equal to about 20 parts by mass based on 100 parts by mass of thepolyimide copolymer in the optical enhancement layer.

The hard coating layer may include a silicon-containing polymer, aurethane-containing polymer, an acrylate-containing polymer, anepoxy-containing polymer, or a combination thereof.

The hard coating layer may include a silicon-containing polymer and thesilicon-based polymer may include organopolysiloxane.

The light transmitting substrate may include polyimide including animide structural unit represented by Chemical Formula 1, or apoly(amide-imide) copolymer including an imide structural unitrepresented by Chemical Formula 1 and an amide structural unitrepresented by Chemical Formula 4, or a combination thereof:

Chemical Formula 1 and Chemical Formula 4 are the same as defined above.

A thickness of the light transmitting substrate may be about 30 μm toabout 300 μm, a thickness of the hard coating layer may be about 1 μm toabout 30 μm, and a thickness of the optical enhancement layer may beabout 0.1 μm to about 10 μm.

The laminated film may have a transmittance of greater than or equal toabout 90%.

The laminated film may have a Yl of less than about 3.

The laminated film may have a haze of less than or equal to about 2.

When a reflectance of the laminated film is measured at an incidentangle of 45 degrees after attaching the laminated film to a blackreflector, an average amplitude of the laminated film in a visible lightregion may be less than or equal to about 0.1%.

Another embodiment provides a display device including the laminatedfilm according to the embodiment.

The laminated film according to an embodiment suppresses the generationof interfacial reflections and interference fringes, thereby improvingoptical characteristics and visibility, and thus exhibits excellentappearance quality, and thus may be usefully used as a window of aflexible display device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a laminated film accordingto an embodiment in which a light transmitting substrate 100, an opticalenhancement layer 200, and a hard coating layer 300 are sequentiallylaminated;

FIG. 2 is a schematic cross-sectional view of a laminated film accordingto another embodiment in which an optical enhancement layer 200, a lighttransmitting substrate 100, and a hard coating layer 300 aresequentially laminated;

FIG. 3 is a schematic cross-sectional view of a laminated film accordingto another embodiment which further includes a rear coating layer 400under the light transmitting substrate 100 of the laminated film of FIG.1;

FIG. 4 is a schematic cross-sectional view of a laminated film accordingto another embodiment which further includes a rear coating layer 400under the optical enhancement layer 200 of the laminated film of FIG. 2;

FIG. 5 is a schematic cross-sectional view of a laminated film accordingto another embodiment which further includes an adhesive or superelasticlayer 500 under the rear coating layer 400 of the laminated film of FIG.3;

FIG. 6 is a schematic cross-sectional view of a laminated film accordingto another embodiment which further includes an adhesive or superelasticlayer 500 under the rear coating layer 400 of the laminated film of FIG.4;

FIG. 7 is a schematic cross-sectional view of a laminated film accordingto another embodiment which further includes an adhesive or superelasticlayer 500 under the light transmitting substrate 100 of the laminatedfilm of FIG. 1;

FIG. 8 is a schematic cross-sectional view of a laminated film accordingto another embodiment which further includes an adhesive or superelasticlayer 500 under the optical enhancement layer 200 of the laminated filmof FIG. 2;

FIG. 9 shows a table containing experimental data of the film of thecontrol group as well as the laminated films manufactured according toComparative Examples 1 and 2 and Example 1, and

FIG. 10 shows a table containing experimental data of the laminatedfilms manufactured according to Examples 2 to 6.

DETAILED DESCRIPTION

Hereinafter, embodiments are described in detail. However, theseembodiments are exemplary, the present invention is not limited theretoand the present invention is defined by the scope of claims.

The invention now will be described more fully hereinafter withreference to the accompanying drawings, in which various embodiments areshown. This invention may, however, be embodied in many different forms,and should not be construed as limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art. Like reference numerals refer tolike elements throughout.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein,“a,” “an,” “the,” and “at least one” do not denote a limitation ofquantity, and are intended to cover both the singular and plural, unlessthe context clearly indicates otherwise. For example, “an element” hasthe same meaning as “at least one element,” unless the context clearlyindicates otherwise. “Or” means “and/or.” As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items. It will be further understood that the terms“comprises” and/or “comprising,” or “includes” and/or “including” whenused in this specification, specify the presence of stated features,regions, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10% or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

As used herein, when specific definition is not otherwise provided,“substituted” refers to replacement of at least one hydrogen of a givenfunctional group by a substituent a halogen atom (F, Cl, Br, or I), ahydroxy group, a nitro group, a cyano group, an amino group —NH₂,—NH(R¹⁰⁰), or —N(R¹⁰¹)(R¹⁰²), wherein R¹⁰⁰, R¹⁰¹, and R¹⁰² are the sameor different, and are each independently a C1 to C10 alkyl group), anamidino group, a hydrazine group, a hydrazone group, a carboxyl group,an ester group, a ketone group, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted alicyclic organic group (e.g.,cycloalkyl group, etc.), a substituted or unsubstituted aryl group(e.g., benzyl group, naphthyl group, fluorenyl group, etc.), asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted alkynyl group, a substituted or unsubstituted heteroarylgroup and a substituted or unsubstituted heterocyclic group, or thesubstituents may be linked with each other to form a ring.

As used herein, when specific definition is not otherwise provided,“alkyl group” refers to a C1 to C30 alkyl group, and specifically a C1to C15 alkyl group, “cycloalkyl group” refers to a C3 to C30 cycloalkylgroup, and specifically a C3 to C18 cycloalkyl group, “alkoxy group”refers to a C1 to C30 alkoxy group, and specifically a C1 to C18 alkoxygroup, “ester group” refers to a C2 to C30 ester group, and specificallya C2 to C18 ester group, “ketone group” refers to a C3 to C30 ketonegroup, and specifically a C3 to C18 ketone group, “aryl group” refers toa C6 to C30 aryl group, and specifically a C6 to C18 aryl group, and“alkenyl group” refers to a C2 to C30 alkenyl group, and specifically aC2 to C18 alkenyl group.

As used herein, when a specific definition is not otherwise provided,the term “aliphatic organic group” refers to a C1 to C30 alkyl group, aC2 to C30 alkenyl group, a C2 to C30 alkynyl group, a C1 to C30 alkylenegroup, a C2 to C30 alkenylene group, or a C2 to C30 alkynylene group,specifically a C1 to C15 alkyl group, a C2 to C15 alkenyl group, a C2 toC15 alkynyl group, a C1 to C15 alkylene group, a C2 to C15 alkenylenegroup, or a C2 to C15 alkynylene group.

As used herein, when a specific definition is not otherwise provided,the term “C3 to C30 alicyclic organic group” refers to a C3 to C30cycloalkyl group, a C3 to C30 cycloalkenyl group, a C3 to C30cycloalkynyl group, a C3 to C30 cycloalkylene group, a C3 to C30cycloalkenylene group, or a C3 to C30 cycloalkynylene group,specifically a C3 to C15 cycloalkyl group, a C3 to C15 cycloalkenylgroup, a C3 to C15 cycloalkynyl group, a C3 to C15 cycloalkylene group,a C3 to C15 cycloalkenylene group, or a C3 to C15 cycloalkynylene group.

As used herein when a definition is not otherwise provided, the term“aromatic organic group” refers to a C6 to C30 group comprising onearomatic ring, two or more aromatic rings fused together to provide acondensed ring system, or a combination thereof (e.g., a single aromaticring or a condensed ring system), linked through a single bond, afluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—,—(CH₂)_(p)—, wherein 1≤p≤10, (CF₂)_(q), wherein 1≤q≤10, —C(CH₃)₂—,—C(CF₃)₂—, and —C(═O)NH—, and specifically through —S(═O)₂—, for examplean aryl group or a C6 to C30 arylene group, specifically a C6 to C16aryl group or a C6 to C16 arylene group such as phenylene. An example ofan aromatic organic group is a fluorenylene group.

As used herein when a definition is not otherwise provided, the term“heteroaromatic organic group” refers to a C2 to C30 group that includesone or more aromatic rings, in which at least one ring member (e.g.,one, two or three ring members) is a heteroatom of N, O, P, Si, Se, Ge,or S. In a C2 to C30 heteroaromatic organic group, the total number ofring carbon atoms ranges from 2 to 30, with remaining ring atoms beingheteroatoms. Multiple rings, if present, may be pendent, spiro or fused.

The term “C1 to C30 alkyl group” as used herein refers to a linear orbranched saturated aliphatic hydrocarbon monovalent group having 1 to 30carbon atoms, and examples thereof include a methyl group, an ethylgroup, a propyl group, an isobutyl group, a sec-butyl group, atert-butyl group, a pentyl group, an isoamyl group, and a hexyl group.The term “C1 to C30 alkylene group” as used herein refers to a divalentgroup having the same structure as the C1 to C30 alkyl group.

The term “C1 to C30 alkoxy group” as used herein refers to a monovalentgroup represented by—OA₁₀₁ (wherein A₁₀₁ is the C1 to C30 alkyl group),and examples thereof include a methoxy group, an ethoxy group, and anisopropyloxy group.

The term “C2 to C30 alkenyl group” as used herein refers to ahydrocarbon group having at least one carbon-carbon double bond in themiddle or at the terminus of the C2 to C30 alkyl group, and examplesthereof include an ethenyl group, a propenyl group, and a butenyl group.The term “C2 to C30 alkenylene group” as used herein refers to adivalent group having the same structure as the C2 to C30 alkenyl group.

The term “C2 to C30 alkynyl group” as used herein refers to ahydrocarbon group having at least one carbon-carbon triple bond in themiddle or at the terminus of the C2 to C30 alkyl group, and examplesthereof include an ethynyl group, and a propynyl group. The term “C2 toC30 alkynylene group” as used herein refers to a divalent group havingthe same structure as the C2 to C30 alkynyl group.

The term “C3 to C30 cycloalkyl group” as used herein refers to amonovalent saturated hydrocarbon monocyclic group having 3 to 30 carbonatoms, and non-limiting examples thereof include a cyclopropyl group, acyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptylgroup, a cyclooctyl group, an adamantyl group, a norbornenyl group, acyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, abicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, abicyclo[2.2.1]heptyl group, and a bicyclo[2.2.2]octyl group. The term“C3 to C30 cycloalkylene group” as used herein refers to a divalentgroup having the same structure as the C3 to C30 cycloalkyl group.

The term “C2 to C30 heterocycloalkyl group” as used herein refers to amonovalent saturated monocyclic group having N, O, P, Si, Se, Ge, S, orany combination thereof as a ring-forming atom and 2 to 30 carbon atoms,and non-limiting examples thereof include a tetrahydrofuranyl group anda tetrahydrothiophenyl group. The term “C2 to C30 heterocycloalkylenegroup” as used herein refers to a divalent group having the samestructure as the C2 to C30 heterocycloalkyl group.

The term “C6 to C30 aryl group” as used herein refers to a monovalentgroup having a carbocyclic aromatic system having 6 to 30 carbon atoms,and the term “C6 to C30 arylene group” as used herein refers to adivalent group having a carbocyclic aromatic system having 6 to 30carbon atoms. Non-limiting examples of the C6 to C30 aryl group includea phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenylgroup, a pyrenyl group, and a chrysenyl group. When the C6 to C30 arylgroup and the C6 to C30 arylene group each include two or more rings,the rings may be fused to each other.

The term “C2 to C30 heteroaryl group” as used herein refers to amonovalent group having a heterocyclic aromatic system that has N, O, P,Si, Se, Ge, S, or any combination thereof as a ring-forming atom, inaddition to 2 to 30 carbon atoms. The term “C2 to C30 heteroarylenegroup” as used herein refers to a divalent group having a heterocyclicaromatic system that has N, O, P, Si, Se, Ge, S, or any combinationthereof as a ring-forming atom, in addition to 2 to 30 carbon atoms.Non-limiting examples of the C2 to C30 heteroaryl group include apyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinylgroup, a triazinyl group, a quinolinyl group, and an isoquinolinylgroup. When the C2 to C30 heteroaryl group and the C2 to C30heteroarylene group each include two or more rings, the rings may befused to each other.

As used herein, when specific definition is not otherwise provided, theterm “combination” refers to mixing or copolymerization. Herein,“copolymerization” refers to a random copolymerization, a blockcopolymerization, or a graft copolymerization.

As used herein, the term “polyimide” refers to “polyimide”, “polyamicacid,” or a combination thereof as well as “polyimide” itself. The terms“polyimide” and “polyamic acid” may be understood to have the samemeanings.

In addition, as used herein, “*” refers to a portion of attachment toother atom or other chemical formula.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it may be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

An embodiment provides a laminated film that may be used as a coverwindow protecting a display device such as a flexible display device ora foldable display device.

A glass substrate has been conventionally used for protecting thedisplay device, but when requiring flexible and foldable characteristicsof freely bending a shape, it is necessary to use a plastic materialhaving hardness and strength as a window of a display device and alsohaving light transmittance, color or the like similar to those of theglass substrate so as to function as a display device. A cover windowfor a display device requires high appearance quality as well as highoptical characteristics, durability, and flexural property.

Research on a use of a polyimide-based transparent film that is aplastic material but has high durability and heat resistance, as well assatisfies optical characteristics to some extent has been studied. Here,a laminated film including a hard coating layer added on a polyimidesubstrate in order to obtain hardness comparable to that of glass hasbeen attempted. However, due to the lamination of the two layers havingdifferent refractive indexes, an interference phenomenon may occur, anda difference of the thickness and refractive index of each layer mayworsen the interference phenomenon and may cause a strong rainbowphenomenon on the film surface. Even though the inherent characteristicsof the material, such as refractive index, of the layers may beidentical, a thickness deviation or a partial mixing of the materials ofthe layers during the film forming process may occur, and may modify therainbow phenomenon. Resultantly, the rainbow phenomenon of an opticalfilm is a phenomenon in which a reflectance varies or the viewing anglechanges depending on a position of the wide region of the film, whichmay be observed with the naked eye.

It is known that a rainbow phenomenon of an optical film does not appearwhen a reflectance ripple amplitude is less than or equal to about 1% inthe wavelength region of about 500 nm to about 600 nm, or when themaximum amplitude is less than 0.5% in an entire visible region.However, since a conventional reflectance measurement is performed in awide measurement range of several millimeters or more, minute changes ofthe reflectance may further occur depending on the position in thevisible wavelength region, and the inherent reflectance ripple thatcauses the rainbow phenomenon may be offset and may not appear. Inaddition, since the reflectance ripple amplitude is measured at areflection angle of less than or equal to about 10°, it may be differentfrom the rainbow phenomenon which is visually measured.

In an embodiment, in a laminated film including a light transmittingsubstrate and a hard coating layer, interfacial reflections andinterference fringes between layers may be suppressed, and thereby alaminated film having improved optical characteristics and visibilitymay be provided. Since an average amplitude is less than or equal to0.1% in a visible region, when a reflectance of the laminated film ismeasured at an incident angle of 45 degrees after attaching thelaminated film to a black reflector, the laminated film according to anembodiment does not exhibit a surface rainbow phenomenon and exhibitsimproved optical characteristics and visibility.

In an embodiment, the laminated film includes a light transmittingsubstrate; a hard coating layer; and an optical enhancement layerdisposed between the light transmitting substrate and the hard coatinglayer or at a position facing the hard coating layer with the lighttransmitting substrate therebetween, wherein the light transmittingsubstrate includes a polyimide, a poly(amide-imide) copolymer, or acombination thereof, and the optical enhancement layer includes acopolymer including a polyimide.

FIGS. 1 and 2 show cross-sections of the laminated film according to anembodiment schematically.

Referring to FIG. 1, an optical enhancement layer 200 including acopolymer including a polyimide may be disposed on a light transmittingsubstrate 100 including a polyimide, a poly(amide-imide) copolymer, or acombination thereof, and a hard coating layer 300 is disposed on theoptical enhancement layer 200.

Referring to FIG. 2, a hard coating layer 300 may be directly disposedon a light transmitting substrate 100 including a polyimide, apoly(amide-imide) copolymer, or a combination thereof, and an opticalenhancement layer 200 including a copolymer including a polyimide may bedisposed at an opposed surface to the surface on which a hard coatinglayer 300 is disposed of the light transmitting substrate 100.

The laminated films according to FIGS. 1 and 2 both include a lighttransmitting substrate 100, a hard coating layer 300, and an opticalimproving layer 200, but there is a difference in the position of theoptical enhancement layer 200 in the laminated films wherein the opticalenhancement layer 200 is disposed between the light transmittingsubstrate 100 and the hard coating layer 300 (FIG. 1) or wherein theoptical enhancement layer 200 faces the hard coating layer 300 with thelight transmission substrate 200 therebetween (FIG. 2). Even though theoptical enhancement layer 200 is disposed at different positions in thelaminated films as above, as clearly shown in the following examples andcomparative examples, in the two cases including optical enhancementlayer 200, when observing the surface of the laminated film, that is,the hard coated surface, the rainbow phenomenon is substantially reducedas compared with the laminated film without the optical enhanced layer200.

Optical enhancement layer 200 may have a refractive index between arefractive index of light transmitting substrate 100 and a refractiveindex of hard coating layer 300. In this case, the laminated filmaccording to an embodiment does not show a rainbow phenomenon, and mayhave improved visibility and optical characteristics.

In an embodiment, the optical enhancement layer 200 may have arefractive index of about 1.5 to about 1.7. When the laminated filmaccording to an embodiment includes a polyimide film as the lighttransmitting substrate 100, and a silicon-containing polymer, aurethane-containing polymer, an acrylate-containing polymer, anepoxy-containing polymer, a polycaprolactone, a urethane-acrylatecopolymer, polyrotaxane, a silica-containing inorganic hard coatingmaterial, or a combination thereof as the hard coating layer 300, arefractive index of the polyimide film is about 1.55 to about 1.75, anda refractive index of the hard coating layer is about 1.5 to about 1.6,such that the optical enhancement layer 200 may be adjusted to have avalue between the refractive indexes of the two layers.

In an embodiment, the light transmitting substrate 100 may have arefractive index of about 1.6 to about 1.75, for example, about 1.65 toabout 1.72, or about 1.67 to about 1.7, the hard coating layer 300 mayhave a refractive index of about 1.5 to about 1.6, for example, about1.5 to about 1.59, about 1.5 to about 1.57, about 1.5 to about 1.55,about 1.5 to about 1.53, or about 1.5 to about 1.52, and the opticalenhancement layer 200 may have a refractive index of about 1.5 to about1.7, for example, greater than 1.5 and less than or equal to about 1.7,for example, about 1.51 to about 1.69, about 1.52 to about 1.68, about1.55 to about 1.65, about 1.57 to about 1.63, about 1.58 to about 1.61,or about 1.58 to about 1.6. As long as the refractive index of theoptical enhancement layer 200 may be between the refractive index of thelight transmitting substrate 100 and the refractive index of the hardcoating layer 300, the refractive index of each layer is not limited tothe above values.

The copolymer including polyimide of the optical enhancement layer mayinclude (a) an imide structural unit, and (b) a urethane structuralunit, a siloxane structural unit, an amide structural unit, or acombination thereof.

For example, the optical enhancement layer may include apoly(imide-urethane) copolymer including an imide structural unit and aurethane structural unit.

The optical enhancement layer may include a poly(imide-siloxane)copolymer including an imide structural unit and a siloxane structuralunit.

The optical enhancement layer may include a poly(imide-amide) copolymerincluding an imide structural unit and an amide structural unit.

The optical enhancement layer may include a copolymer including (a) animide structural unit, and (b) at least two structural units of aurethane structural unit, a siloxane structural unit, and an amidestructural unit.

The optical enhancement layer may include a copolymer including an imidestructural unit, a urethane structural unit, a siloxane structural unit,and an amide structural unit.

The imide structural unit may be represented by Chemical Formula 1:

In Chemical Formula 1,

D is a substituted or unsubstituted quadrivalent C4 to C30 alicyclicorganic group, a substituted or unsubstituted quadrivalent C6 to C30aromatic organic group, or a substituted or unsubstituted quadrivalentC4 to C30 heteroaromatic organic group, or a combination thereof, and

the alicyclic organic group, the aromatic organic group, theheteroaromatic organic group, or the combination thereof may be a singlering, a condensed ring in which at least two rings are fused, or a ringsystem including at least two rings of the single ring and the condensedring, wherein the at least two rings are linked by a single bond, or afluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—,—(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.

D of Chemical Formula 1 may be Chemical Formulae of Group 1:

In the Chemical Formulae of Group 1,

each of Chemical Formulae Group 1 may be substituted or unsubstituted,each L may be the same or different and may each independently be asingle bond, a fluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—,—S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—,—C(C_(n)F_(2n+1))₂—, —(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof,

* is a linking point with an adjacent atom,

Z¹ and Z² may be the same or different and each independently be —N═ or—C(R¹⁰⁰)═, wherein R¹⁰⁰ is hydrogen or a C1 to C5 alkyl group, Z¹ and Z²are not simultaneously —C(R¹⁰⁰)═, and

Z³ is —O—, —S—, or —NR¹⁰¹—, wherein R¹⁰¹ is hydrogen or a C1 to C5 alkylgroup.

The Chemical Formulae of Group 1 may be represented by the ChemicalFormulae of Group 2, but are not limited thereto:

In an embodiment, the imide structural unit represented by ChemicalFormula 1 may be represented by Chemical Formula 1-1:

In Chemical Formula 1-1, L is the same as defined in the ChemicalFormulae of Group 1.

In an exemplary embodiment, the imide structural unit represented byChemical Formula 1 may be represented by Chemical Formula 1-1, wherein Lis at least one of a single bond, —C(C_(n)H_(2n+1))₂—,—C(C_(n)F_(2n+1))₂—, —(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—, or—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10, and1≤q≤10), for example, Chemical Formula 1-1 may be a combination of Lbeing a single bond and L being —C(C_(n)F_(2n+1))₂— (wherein 1≤n≤10).

In an embodiment, Chemical Formula 1-1 L may be a combination of asingle bond and —C(CF₃)₂—.

The urethane structural unit may be represented by Chemical Formula 2:

*—(—Y—NH—CO—O—Z—)—*   (Chemical Formula 2)

In Chemical Formula 2,

Y and Z are each independently a substituted or unsubstituted divalentC1 to C30 aliphatic organic group, a substituted or unsubstituteddivalent C3 to C30 alicyclic organic group, a substituted orunsubstituted C6 to C30 aromatic organic group, or a substituted orunsubstituted C2 to C30 heteroaromatic organic group, or a combinationthereof, and

the alicyclic organic group, the aromatic organic group, theheteroaromatic organic group, or the combination thereof may be a singlering, a condensed ring in which at least two rings are fused, or a ringsystem including at least two rings of the single ring and the condensedring, wherein the at least two rings are linked by a single bond, afluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—,—(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.

In an embodiment, Y may be a substituted or unsubstituted divalentalicyclic organic group, or a substituted or unsubstituted divalentaromatic organic group, for example, a substituted divalent alicyclicorganic group.

In an embodiment, Z may be a substituted or unsubstituted divalent C1 toC30 aliphatic organic group, or a substituted or unsubstituted divalentC6 to C30 aromatic organic group, for example, a substituted orunsubstituted divalent C1 to C20 aliphatic organic group. In anembodiment, Z may be a substituted or unsubstituted divalent C1 to C10alkylene group.

The siloxane structural unit may be represented by Chemical Formula 3:

In Chemical Formula 3,

R^(a) to R^(f) are each independently a substituted or unsubstituted C1to C30 alkyl group, a substituted or unsubstituted C2 to C30 alkenylgroup, a substituted or unsubstituted C2 to C30 alkynyl group, asubstituted or unsubstituted C1 to C30 alkoxy group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC6 to C30 aryl group, an epoxy group-containing group, or a combinationthereof,

L¹ and L² are each independently a single bond, —O—, a substituted orunsubstituted C1 to C30 alkylene group, a substituted or unsubstitutedC1 to C30 heteroalkylene group, a substituted or unsubstituted C2 to C30alkenylene group, a substituted or unsubstituted C3 to C30 cycloalkylenegroup, a substituted or unsubstituted C2 to C30 heterocycloalkylenegroup, a substituted or unsubstituted C6 to C30 aryl group, asubstituted or unsubstituted C2 to C30 heteroaryl group, or acombination thereof, and

m is an integer from 0 to 150.

In an embodiment, R^(a) to R^(f) of Chemical Formula 3 may eachindependently be a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C6 to C30 aryl group, or a combinationthereof, L¹ and L² may each independently be a single bond, —O—, asubstituted or unsubstituted C1 to C30 alkylene group, a substituted orunsubstituted C6 to C30 arylene group, or a combination thereof, and mmay be an integer from 0 to 30.

In an embodiment, R^(a) to R^(f) of Chemical Formula 3 may eachindependently be a substituted or unsubstituted C1 to C4 alkyl group, asubstituted or unsubstituted phenyl group, or a combination thereof, L¹and L² may each independently be a single bond, —O—, a substituted orunsubstituted C1 to C10 alkylene group, a substituted or unsubstitutedphenylene group, or a combination thereof, and m may be an integer from0 to 10.

The amide structural unit may be represented by Chemical Formula 4:

In Chemical Formula 4,

A, E¹, and E² are each independently a substituted or unsubstituteddivalent C1 to C30 aliphatic organic group, a substituted orunsubstituted divalent C3 to C30 alicyclic organic group, a substitutedor unsubstituted divalent C6 to C30 aromatic organic group, asubstituted or unsubstituted divalent C2 to C30 heteroaromatic organicgroup, or a combination thereof, and

the alicyclic organic group, aromatic organic group, heteroaromaticorganic group, or the combination thereof is a single ring, a condensedring in which at least two rings are fused, or a ring system includingat least two rings of the single ring and the condensed ring, whereinthe at least two rings are linked by a single bond, a fluorenylenegroup, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—,—(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.

In an embodiment, A may be a substituted or unsubstituted divalent C6 toC30 aromatic organic group, wherein the aromatic organic group may be asingle ring, a condensed ring in which at least two rings are fused, ora ring system including at least two rings of the single ring and thecondensed ring, wherein the at least two rings are linked by a singlebond, or —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—,—(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10, and1≤q≤10), —C(CF₃, C₆H₅)—, —C(═O )NH—, or a combination thereof.

In an embodiment, A may be of Chemical Formulae of Group 3:

In the Chemical Formulae of Group 3,

R¹⁸ to R²⁹ are the same or different, and are each independentlydeuterium, a halogen, a substituted or unsubstituted C1 to C10 aliphaticorganic group, or a substituted or unsubstituted C6 to C20 aromaticorganic group,

n11 and n14 to n20 are each independently an integer ranging from 0 to4, and

n12 and n13 are each independently an integer ranging from 0 to 3.

In an embodiment, A may be of Chemical Formulae of Group 4:

In an embodiment, A may be a substituted or unsubstituted phenylenegroup, a substituted or unsubstituted biphenylene group, or acombination thereof.

In an embodiment, E¹ and E² may each independently be a substituted orunsubstituted divalent C6 to C30 aromatic organic group, wherein thesubstituted or unsubstituted divalent C6 to C30 aromatic organic groupmay be a single ring, a condensed ring in which at least two rings arefused, or a ring system including at least two rings of the single ringand the condensed ring, wherein the at least two rings are linked by asingle bond, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—,—(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10, and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.

In an embodiment, E¹ and E² may each independently be a group includingat least two substituted or unsubstituted aromatic single rings linkedby a single bond, a substituted or unsubstituted at least two aromaticsingle rings linked by —O—, —S—, —(CH₂)_(p)—, or —(CF₂)_(q)— (wherein1≤p≤10 and 1≤q≤10), or a combination thereof. In an embodiment, E¹ andE² may each independently be at least two phenylene groups that arerespectively substituted with an electron withdrawing group, forexample, a haloalkyl group, for example, a trifluoromethyl group,wherein the at least two phenylene groups are linked by a single bond,at least two phenylene groups that are respectively substituted with analkyl group substituted with a hydroxyl group and a haloalkyl group, forexample, a methyl group substituted with a hydroxyl group and atrifluoromethyl group wherein the at least two phenylene groups arelinked by an alkylene group, for example, a methylene group, or acombination thereof.

In an embodiment, E¹ and E² may each independently be a grouprepresented by Chemical Formula 7 or Chemical Formula 8:

In an embodiment, the copolymer including a polyimide of the opticalenhancement layer may include (a) an imide structural unit, and astructural unit consisting of (b) an urethane structural unit, asiloxane structural unit, an amide structural unit, or a combinationthereof, in a molar ratio (a:b) of about 30:70 to about 90:10. Forexample, the molar ratio of the (a) imide structural unit to astructural unit consisting of (b) an urethane structural unit, asiloxane structural unit, an amide structural unit, or a combinationthereof may be of about 35:65 to about 85:15, for example, about 40:60to about 80:20, about 45:55 to about 75:25, about 50:50 to about 70:30,or about 50:50 to about 60:40.

The copolymer including a polyimide including (a) an imide structuralunit and a structural unit consisting of (b) an urethane structuralunit, a siloxane structural unit, an amide structural unit, or acombination thereof in the above molar ratio may be prepared such thatthe optical enhancement layer 200 may have a refractive index betweenthe light transmitting substrate 100 and the hard coating layer 300 inthe laminated film according to an embodiment.

The optical enhancement layer 200 may further include a partiallycondensed (incompletely condensed) polyhedral oligomer silsesquioxane(POSS) including a functional group capable of forming a hydrogen bondat the broken site of at least one —Si—O—Si— bond, in addition to thepolyimide copolymer including the (a) imide structural unit and thestructural unit including (b) an urethane structural unit, a siloxanestructural unit, an amide structural unit, or a combination thereof.

In an embodiment, the partially condensed polyhedral oligomersilsesquioxane including a functional group capable of forming ahydrogen bond at the broken site of at least one —Si—O—Si— bond may berepresented by Chemical Formula 5 or Chemical Formula 6:

In Chemical Formula 5 and Chemical Formula 6,

R is each independently a substituted or unsubstituted C1 to C30 alkylgroup, a substituted or unsubstituted C3 to C30 cycloalkyl group, asubstituted or unsubstituted C6 to C30 aryl group, or a combinationthereof, and

R′ is each independently —OH, —SH, or —NH₂.

When the optical enhancement layer 200 further includes the partiallycondensed polyhedral oligomer silsesquioxane such as Chemical Formula 5or Chemical Formula 6 including a functional group capable of forming ahydrogen bond at the broken site of a —Si—O—Si— bond of the partiallycondensed polyhedral oligomer silsesquioxane, the optical enhancementlayer may have increased mechanical strengths of the layer, loweredyellowness, and excellent mechanical properties and optical properties.

The partially condensed polyhedral oligomer silsesquioxane including afunctional group capable of forming a hydrogen bond at the broken siteof at least one —Si—O—Si— bond may be included in an amount of less thanor equal to about 20 parts by mass based on 100 parts by mass of thepolyimide copolymer in the optical enhancement layer, for example, lessthan or equal to about 15 parts by mass based on 100 parts by mass ofthe polyimide copolymer, less than or equal to about 10 parts by massbased on 100 parts by mass of the polyimide copolymer, or about 1 partby mass to about 10 parts by mass based on 100 parts by mass of thepolyimide copolymer in the optical enhancement layer 200.

In an embodiment, R of Chemical Formula 5 and Chemical Formula 6 mayeach independently be a substituted or unsubstituted C1 to C10 alkylgroup, a substituted or unsubstituted C3 to C10 cycloalkyl group, asubstituted or unsubstituted C6 to C10 aryl group, or a combinationthereof, and R′ may each independently be —OH or —NH₂.

In an embodiment, R of Chemical Formula 5 and Chemical Formula 6 mayeach independently be a phenyl group, a C1 to C4 alkyl group, or acombination thereof and R′ may be —OH.

In an embodiment, the partially condensed polyhedral oligomersilsesquioxane represented by Chemical Formula 5 and Chemical Formula 6may be represented by Chemical Formula 5-1 and Chemical Formula 6-1,respectively:

In another embodiment, the optical enhancement layer 200 may furtherinclude an additive having a light absorbing function for improvingvisibility and quality of the laminated film according to an embodiment.As the additive having a light absorbing function, for example, a bluingagent and the like may be included. The bluing agent is an additive thatabsorbs light in a wavelength region such as orange to yellow in thevisible light region and adjusts a color. Examples thereof may includeinorganic dyes and pigments such as gamma-ray treated dyes and pigments,cadmium blue and cobalt blue, for example, and organic dyes and pigmentssuch as a phthalocyanine-based bluing agent and a condensed polycyclicbluing agent. The bluing agent is not particularly limited, but acondensed polycyclic bluing agent such as an anthraquinone type bluingagent may be used for heat resistance, light resistance, and solubilityconsiderations. When considering heat resistance, a material having athermal decomposition temperature of greater than or equal to about 200°C. may be used. Examples of the condensed polycyclic bluing agentsinclude, but are not limited to, an anthraquinone-based bluing agent, anindigo-based bluing agent, a phthalocyanine-based bluing agent, and thelike, but are not limited thereto. The bluing agent may appropriately bethose used as a bluing agents in a resin material field.

When the optical enhancement layer 200 includes the bluing agent, anamount of the bluing agent may be selected to depending on types of thebluing agent, but for example, may be included in an amount of greaterthan or equal to about 0.01 parts by mass, for example greater than orequal to about 0.02 parts by mass, or greater than or equal to about0.03 parts by mass, and less than or equal to about 1.0 part by mass,for example, less than or equal to about 0.5 parts by mass, less than orequal to about 0.2 parts by mass based on 100 parts by mass of the solidof the polyimide copolymer of the optical enhancement layer 200.

A thickness of the optical enhancement layer may be about 0.1 μm toabout 10 μm, for example, about 0.1 μm to about 8 μm, about 0.1 μm toabout 7 μm, about 0.1 μm to about 5 μm, about 0.3 μm to about 5 μm,about 0.5 μm to about 5 μm, about 0.5 μm to about 3 μm, about 0.5 μm toabout 2.5 μm, about 0.5 μm to about 2 μm, about 0.5 μm to about 1.5 μm,or about 1 μm.

The light transmitting substrate 100 of the laminated film according toan embodiment may include a polyimide and/or a poly(imide-amide)copolymer.

A polyimide or a poly (amide-imide) copolymer film is useful for displaysubstrate material due to its high light transmittance, thermalstability, mechanical strength, flexibility, and the like. In thisregard, recently there have been attempts to use it as a window filmreplacing the top-most glass of a mobile device, such as, a smart phoneor a tablet PC, and thus a film having much improved mechanicalproperties and optical properties are desirable. Meanwhile, a refractiveindex of such a polyimide or a poly (imide-amide) copolymer film ishigher than that of a cellulose ester film, for example, a cellulosetriacetate film. Accordingly, when a polyimide or poly(imide-amide)copolymer film is used as a light transmitting substrate of a windowfilm, a rainbow phenomenon by interfacial reflection and opticalinterference may occur due to a refractive index difference with a hardcoating layer having a low refractive index which is disposed on thelight transmitting substrate to compensate mechanical properties of thelight transmitting substrate. In an embodiment, by introducing theoptical enhancement layer 200 as described above, a rainbow phenomenonof the laminated film including the light transmitting substrate 100including polyimide or a poly(imide-amide) copolymer and the hardcoating layer 300 applied to strengthen the light transmitting substrate100 may be substantially reduced or prevented, and thus an opticallaminate having improved optical characteristics and color visibilitymay be provided.

In the laminated film according to an embodiment, a polyimide or apoly(imide-amide) copolymer used for the light transmitting substrate100 is not particularly limited as long as it has mechanical propertiesand optical properties that are appropriate for an optical film, forexample, a window film. Various types of polyimide or poly(imide-amide)copolymers known in this field may be used without limitation. In anembodiment, the polyimide or poly(imide-amide) copolymer havingexcellent optical properties and mechanical properties may include apolyimide including an imide structural unit represented by ChemicalFormula 1, and/or, a poly(imide-amide) copolymer including an amidestructural unit represented by Chemical Formula 4, as well as the imidestructural unit:

Chemical Formula 1 and Chemical Formula 4 are the same as describedabove, and thus detailed descriptions thereof will be omitted.

In an embodiment, the imide structural unit represented by ChemicalFormula 1 may include an imide structural unit represented by ChemicalFormula 1-1, but is not limited thereto:

In Chemical Formula 1-1,

L is the same or different and each independently is a single bond, afluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—,—(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤p≤10), —C(CF₃)(C₆H₅)—, or —C(═O)NH—, and

* is a linking point with an adjacent atom.

In an embodiment, in Chemical Formula 1-1, L may be a combination of asingle bond and —C(CF₃)₂—, but is not limited thereto.

In an embodiment, the amide structural unit represented by ChemicalFormula 4 may be an amide structural unit wherein A of Chemical Formula4 is a substituted or unsubstituted phenylene group, a substituted orunsubstituted biphenylene group, or a combination thereof, and E¹ and E²are each independently a group represented by Chemical Formula 7, agroup represented by Chemical Formula 8, or a combination thereof, butis not limited thereto:

The light transmitting substrate 100 may further include a partiallycondensed (incompletely condensed) polyhedral oligomer silsesquioxane(POSS) including a functional group capable of forming a hydrogen bondat the broken site of at least one —Si—O—Si— bond, in addition to apolyimide including an imide structural unit, or a poly(imide-amide)copolymer including an imide structural unit and an amide structuralunit.

In an embodiment, the partially condensed polyhedral oligomersilsesquioxane including a functional group capable of forming ahydrogen bond at the broken site of at least one —Si—O—Si— bond may berepresented by

Chemical Formula 5 or Chemical Formula 6:

In Chemical Formula 5 and Chemical Formula 6,

R is each independently a substituted or unsubstituted C1 to C30 alkylgroup, a substituted or unsubstituted C3 to C30 cycloalkyl group, asubstituted or unsubstituted C6 to C30 aryl group, or a combinationthereof, and

R′ is each independently —OH, —SH, or —NH₂.

The partially condensed polyhedral oligomer silsesquioxane including afunctional group capable of forming a hydrogen bond at the broken siteof at least one —Si—O—Si— bond are the same as described above and thusdetailed descriptions thereof will be omitted.

The light transmitting substrate 100 including a polyimide or apoly(imide-amide) copolymer may further include the partially condensedpolyhedral oligomer silsesquioxane including a functional group capableof forming a hydrogen bond at the broken site of at least one —Si—O—Si—bond, like the optical enhancement layer 200, and thereby mechanicalstrength and optical properties may be further improved.

The partially condensed polyhedral oligomer silsesquioxane including afunctional group capable of forming a hydrogen bond at the broken siteof at least one —Si—O—Si— bond may be present in an amount of less thanor equal to about 20 parts by mass based on 100 parts by mass of thepolyimide or poly(imide-amide) copolymer in the optical enhancementlayer, for example, less than or equal to about 15 parts by mass basedon 100 parts by mass of the polyimide copolymer, less than or equal toabout 10 parts by mass based on 100 parts by mass of the polyimidecopolymer, or about 1 part by mass to about 10 parts by mass based on100 parts by mass of the polyimide or the poly(imide-amide) copolymer inthe light transmitting substrate 100.

A thickness of the light transmitting substrate may be about 10 μm toabout 300 μm, for example, about 15 μm to about 300 μm, about 20 μm toabout 300 μm, about 25 μm to about 300 μm, about 30 μm to about 300 μm,about 30 μm to about 250 μm, about 30 μm to about 200 μm, about 30 μm toabout 150 μm, about 30 μm to about 100 μm, about 30 μm to about 80 μm,about 30 μm to about 70 μm, about 30 μm to about 60 μm, about 35 μm toabout 60 μm, or about 35 μm to about 55 μm.

The hard coating layer 300 applied to the laminated film according to anembodiment may be any known hard coating layer material in the field andis not particularly limited. The hard coating layer may increase asurface hardness of the laminated film.

As a material of the hard coating layer 300, a material that is cured byheat or light may be used, for example, an acrylate-containing polymer,a urethane-containing polymer, an epoxy-containing polymer, asilicon-containing polymer, polycaprolactone, a urethane-acrylatecopolymer, polyrotaxane, a silica-containing inorganic hard coatingmaterial, and the like, but is not limited thereto. Theacrylate-containing polymer may be a polymer of a monomer mixtureincluding a multi-functional acrylate monomer. Examples of themulti-functional acrylate monomer may be trimethylolpropane triacrylate(TMPTA), trimethylolpropaneethoxy triacrylate (TMPEOTA), propoxylatedglycerol triacrylate (GPTA), pentaerythritol tetraacrylate (PETA), anddipentaerythritol hexaacrylate (DPHA), but are not limited thereto. Theurethane-containing or acrylate-containing polymer and the polymer ofthe monomer mixture including the multi-functional acrylate may exhibitexcellent adherence and high productivity.

In an embodiment, the hard coating layer may include thesilicon-containing polymer, and the silicon-containing polymer mayinclude an organopolysiloxane such as silsesquioxane.

Although in FIGS. 1 and 2, the hard coating layer 300 is a single layer,the hard coating layer is not so limited and may have a multi-layerstructure of at least two layers.

A thickness of the hard coating layer 300 may be less than or equal toabout 50 μm, for example about 1 μm to about 50 μm, about 1 μm to about40 μm, about 1 μm to about 30 μm, about 3 μm to about 30 μm, about 5 μmto about 30 μm, about 5 μm to about 25 μm, about 5 μm to about 20 μm,about 5 μm to about 15 μm, or about 5 μm to about 10 μm, but is notlimited thereto.

The laminated film according to an embodiment may further include anylayer for improving optical properties, mechanical properties, and/orflexural characteristics of the laminated film, in addition to the lighttransmitting substrate 100, the optical enhancement layer 200, and thehard coating layer 300.

For example, as shown in FIGS. 3 and 4, the laminated film according toan embodiment may further include a rear coating layer 400 disposedunder the light transmitting substrate 100. In the case of FIG. 3, therear coating layer 400 is added under the light transmitting substrate100 of the laminated film of FIG. 1. FIG. 4 shows a rear coating layer400 disposed under the light transmitting base 100 of the laminated filmof FIG. 2. In the laminated film of FIG. 2, the optical enhancementlayer 200 exists under the light transmitting substrate 100, and asshown in FIG. 4, the rear coating layer 400 is substantially disposedunder the optical enhancement layer 200 that is disposed under the lighttransmitting substrate 100.

The rear coating layer 400 may include any material as long as it may beoptically colorless and transparent, adheres well to an adhesive layeror a superelastic layer that will be described later, and may maintainflexural properties of the laminated film. For example, the rear coatinglayer 400 may include the same material as the hard coating layer 300,and any material used for a hard coating layer of a conventional windowfor a display device may be selected without limitation. For example,the rear coating layer 400 may include a (meth)acrylate-containingpolymer, polycaprolactone, a urethane-acrylate copolymer, polyrotaxane,an epoxy resin, a siloxane copolymer, perfluoropolyether, or acombination thereof.

A thickness of the rear coating layer 400 may be about 30 nm to about300 nm, for example, about 40 nm to about 200 nm, about 50 nm to about180 nm, about 60 nm to about 150 nm, about 70 nm to about 130 nm, about80 nm to about 120 nm, or about 90 nm to about 120 nm, and may berelatively smaller than the hard coating layer 300.

A refractive index of the rear coating layer may be less than or equalto about 1.7, for example, less than or equal to about 1.6, less than orequal to about 1.5, less than or equal to about 1.4, or less than orequal to about 1.3.

The light transmitting substrate 100, the optical enhancement layer 200,and the hard coating layer 300 are the same as those described withreference to FIGS. 1 and 2, and detailed description thereof will beomitted.

As described above, the laminated film may further include an adhesivelayer or a superelastic layer 500 under the rear coating layer 400. FIG.5 is a schematic view of a structure including an adhesive layer or asuper-elastic layer 500 under the rear coating layer 400 of thelaminated film of FIG. 3, and FIG. 6 is a view of a structure furtherincluding an adhesive layer or a superelastic layer 500 under the rearcoating layer 400 of the laminated film of FIG. 4.

Meanwhile, the laminated film according to an embodiment may not includethe rear coating layer 400, but may include an adhesive layer or asuper-elastic layer 500 under the light transmitting substrate 100. Thisis schematically shown in FIGS. 7 and 8.

FIG. 7 is a schematic view of the laminated film further including anadhesive layer or superelastic layer 500 under the light transmittingsubstrate 100 in the laminated film of FIG. 1, and FIG. 8 is a schematicview of the laminated film including the optical enhancement layer 200under the light transmitting substrate 100 and further including anadhesive layer or superelastic layer 500 under the optical enhancementlayer 200. That is, the laminated film according to one embodiment mayfurther include an adhesive layer or a superelastic layer 500 under thelight transmitting substrate 100 with or without the rear coating layer400. By further including the adhesive layer or the superelastic layer500, the laminated film may be adhered to a front surface of a displaydevice or to an additional film.

The adhesive layer may include a pressure-sensitive adhesive (PSA), andthe superelastic layer may include a superelastic material such aspolyurethane, polydimethylsiloxane (PDMS), but they are not limited to.

On the other hand, the adhesive layer or the superelastic layer 500 maycause deterioration of optical characteristics and hardness, so a thinadhesive layer or the superelastic layer 500 may be preferred. Forexample, the thickness of the adhesive layer or the superelastic layer500 may be less than or equal to about 50 μm, for example, about 10 μmto about 40 μm, or about 10 μm to about 30 μm, but is not limitedthereto.

The light transmitting substrate 100, the optical enhancement layer 200,and the hard coating layer 300, and the rear coating layer 400 are thesame as described above, and a detailed description thereof is omitted.

As shown in FIGS. 1 to 8, the laminated films according to embodimentsmay further include any layer for a desired application, according tothe desired characteristics, such as the rear coating layer 400, or theadhesive layer or the superelastic layer 500, and the like, in additionto the light transmitting substrate 100, the optical enhancement layer200, and the hard coating layer 300, and thus mechanical properties,optical properties, and/or flexural characteristics of the laminatedfilm may be further improved or supplemented. A person skilled in thisart may produce the laminated films according to embodiments byselecting, combining, and modifying the above-described layers andlayers known in the art in various forms depending on intended uses andfunctions and the various forms of selection, combination, andmodification are also within the scope of the present disclosure.

According to an embodiment, the laminated film including the lighttransmitting substrate 100, the optical enhancement layer 200, and thehard coating layer 300 may have a light transmittance of greater than orequal to about 90% in an entire wavelength range of about 350 nm toabout 750 nm, a yellowness index (YI) of less than about 3, and a hazeof less than or equal to about 2. In addition, the laminated filmaccording to an embodiment does not show a rainbow phenomenon on thesurface when viewed with a naked eye, and when the reflectance ismeasured at an incident angle of 45 degrees after attaching thelaminated film to a black reflector, the average amplitude in thevisible region is less than or equal to about 0.1%, which indicates thatthe rainbow phenomenon is suppressed.

That is, in the laminated film including the light transmittingsubstrate 100 and the hard coating layer 300 having different refractiveindexes, the laminated film may have excellent optical properties andmay suppress the rainbow phenomenon on the surface and thus improveappearance quality, by including the optical enhancement layer includinga polyimide-based copolymer having a refractive index between therefractive index values of the two layers between the light transmittingsubstrate 100 and the hard coating layer 300 or at a position facing thehard coating layer 300 with the light transmitting substrate 100therebetween.

The laminated film according to an embodiment may be manufactured byproducing a film including a polyimide or a poly(imide-amide) copolymeras the light transmitting substrate 100, applying a coating of asolution of a polyimide-containing copolymer for forming the opticalenhancement layer 200 on one surface of the light transmitting substrate100, removing a solvent from the coated product to form the opticalenhancement layer 200, subsequently, applying a coating a hard coatingsolution for forming the hard coating layer 300 on the surface of theoptical enhancement layer 200 or on the other surface of the lighttransmitting substrate 100 opposed to the surface on which the opticalenhancement layer 200 is disposed, and removing the solvent from thehard coating solution to form the hard coating layer 300.

The film including the polyimide or poly(imide-amide) copolymer as thelight transmitting substrate 100 may be easily produced by preparing thepolyimide and/or poly(imide-amide) copolymer using a method of preparingthe polyimide and/or poly(imide-amide) copolymer known in this art, andthen making a film therefrom, or may be a commercially availablepolyimide or poly(imide-amide) copolymer film.

The imide structural unit of the polyimide or poly(imide-amide)copolymer may be prepared by a polymerization reaction of diamine anddianhydride or a diisocyanate compound in an organic solvent. Thediamine, dianhydride, and diisocyanate are not limited to specificcompounds, and any diamine, dianhydride, and diisocyanate compound canbe appropriately selected and used as long as they may provide polyimideor a poly(imide-amide) copolymer satisfying optical properties andmechanical properties suitable for use as the light transmittingsubstrate 100 of the laminated film according to an embodiment. Examplesof the diamine compound may be hexamethylene diamine; m-phenylenediamine; p-phenylene diamine; 1,3-bis(4-aminophenyl) propane;2,2-bis(4-aminophenyl) propane; 4,4′-diamino-diphenyl methane;1,2-bis(4-aminophenyl) ethane; 1,1-bis(4-aminophenyl) ethane;2,2′-diamino-diethyl sulfide; bis(4-aminophenyl) sulfide;2,4′-diamino-diphenyl sulfide; bis(3-aminophenyl) sulfone;bis(4-aminophenyl) sulfone; 4,4′-diamino-dibenzyl sulfoxide;bis(4-aminophenyl) ether; bis(3-aminophenyl) ether;bis(4-aminophenyl)diethyl silane; bis(4-aminophenyl) diphenyl silane;bis(4-aminophenyl) ethyl phosphineoxide; bis(4-aminophenyl) phenylphosphineoxide; bis(4-aminophenyl)-N-phenyl amine;bis(4-aminophenyl)-N-methylamine; 1,2-diamino-naphthalene,1,4-diamino-naphthalene, 1,5-diamino-naphthalene;1,6-diamino-naphthalene, 1,7-diamino-naphthalene,1,8-diamino-naphthalene; 2,3-diamino-naphthalene;2,6-diamino-naphthalene; 1,4-diamino-2-methyl-naphthalene;1,5-diamino-2-methyl-naphthalene, 1,3-diamino-2-phenyl-naphthalene;4,4′-diamino-biphenyl; 3,3′-diamino-biphenyl;3,3′-dichloro-4,4′-diamino-biphenyl;3,3′-dimethyl-4,4′-diamino-biphenyl,3,3′-dimethyl-4,4′-diamino-biphenyl;3,3′-dimethoxy-4,4′-diamino-biphenyl; 4,4′-bis(4-aminophenoxy)-biphenyl;2,4-diamino-toluene; 2,5-diamino-toluene; 2,6-diamino-toluene;3,5-diamino-toluene; 1,3-diamino-2,5-dichloro-benzene,1,4-diamino-2,5-dichloro-benzene; 1-methoxy-2,4-diamino-benzene;1,4-diamino-2-methoxy-5-methyl-benzene,1,4-diamino-2,3,5,6-tetramethyl-benzene,1,4-bis(2-methyl-4-amino-pentyl)-benzene;1,4-bis(1,1-dimethyl-5-amino-pentyl)-benzene;1,4-bis(4-aminophenoxy)-benzene, o-xylene diamine; m-xylene diamine;p-xylene diamine; 3,3′-diamino-benzophenone; 4,4′-diamino-benzophenone;2,6-diamino-pyridine; 3,5-diamino-pyridine; 1,3-diamino-adamantane,bis[2-(3-aminophenyl)hexafluoroisopropyl] diphenyl ether;3,3′-diamino-1,1,1′-diadamantane, N-(3-aminophenyl)-4-aminobenzamide;4-aminophenyl-3-aminobenzoate; 2,2-bis(4-aminophenyl) hexafluoropropane;2,2-bis(3-aminophenyl) hexafluoropropane;2-(3-aminophenyl)-2-(4-aminophenyl)hexafluoropropane;2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropane;2,2-bis[4-(2-chloro-4-aminophenoxy)phenyl hexafluoropropane;1,1-bis(4-aminophenyl)-1-phenyl -2,2,2-trifluoroethane;1,1-bis[4-(4-aminophenoxy)phenyl]-1-phenyl-2,2,2-trifluoroethane;1,4-bis(3-aminophenyl)buta-1-ene-3-yn, 1,3-bis(3-aminophenyl)hexafluoropropane; 1,5-bis(3-aminophenyl) decafluoropentane; and4,4′-bis[2-(4-aminophenoxyphenyl) hexafluoroisopropyl] diphenyl ether,diaminocyclohexane, bicyclohexyldiamine, 4,4′-diaminocyclohexylmethane,diaminofluorene, and the like, but are not limited thereto. Such diaminecompounds may be commercially available or may be synthesized by knownmethods.

For example, the diamine may be compounds with the following structuralformulae:

In an embodiment, the diamine may be 2,2′-bis(trifluoromethyl)benzidine(TFDB) and/or3,3′-bis(1-hydroxy-1-trifluoromethyl-2,2,2-trifluoroethyl)-4,4′-methylenedianiline(MFA-MDA).

The dianhydride may be a tetracarboxylic dianhydride 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA),bicycle[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTDA),3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride (DSDA),4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA),4,4′-oxydiphthalic anhydride (ODPA), pyromellitic dianhydride (PMDA),4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicanhydride (DTDA), 1,2,4,5-benzene tetracarboxylic dianhydride;1,2,3,4-benzene tetracarboxylic dianhydride;1,4-bis(2,3-dicarboxyphenoxy) benzene dianhydride;1,3-bis(3,4-dicarboxyphenoxy) benzene dianhydride; 1,2,4,5-naphthalenetetracarboxylic dianhydride; 1,2,5,6-naphthalene tetracarboxylicdianhydride; 1,4,5,8-naphthalene tetracarboxylic dianhydride;2,3,6,7-naphthalene tetracarboxylic dianhydride;2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;3,3′,4,4′-biphenyl tetracarboxylic dianhydride; 2,2′,3,3′-biphenyltetracarboxylic dianhydride; 4,4′-bis(3,4-dicarboxyphenoxy)diphenyldianhydride; bis(2,3-dicarboxylphenyl) ether dianhydride;4,4′-bis(2,3-dicarboxyphenoxy) diphenylether dianhydride;4,4′-bis(3,4-dicarboxyphenoxy) diphenylether dianhydride;bis(3,4-dicarboxylphenyl) sulfide dianhydride;4,4′-bis(2,3-dicarboxyphenoxy) diphenylsulfide dianhydride;4,4′-bis(3,4-dicarboxyphenoxy) diphenyl sulfide dianhydride;bis(3,4-dicarboxylphenyl) sulfone dianhydride;4,4′-bis(2,3-dicarboxyphenoxy) diphenylsulfone dianhydride;4,4′-bis(3,4-dicarboxylphenoxy) diphenylsulfone dianhydride;3,3′,4,4″-benzophenone tetracarboxylic acid dianhydride;2,2′,3,3′-benzophenone tetracarboxylic acid dianhydride;2,3,3′4′-benzophenone tetracarboxylic acid dianhydride;4,4′-bis(3,4-dicarboxylphenoxy) benzophenone dianhydride;bis(2,3-dicarboxylphenyl) m ethane dianhydride;bis(3,4-dicarboxylphenyl) methane dianhydride;1,1-bis(2,3-dicarboxylphenyl) ethane dianhydride;1,1-bis(3,4-dicarboxylphenyl) ethane dianhydride;1,2-bis(3,4-dicarboxylphenyl) ethane dianhydride;2,2-bis(2,3-dicarboxylphenyl) propane dianhydride;2,2-bis(3,4-dicarboxylphenyl) propane dianhydride;2,2-bis[4-(2,3-dicarboxylphenoxy) phenyl] propane dianhydride;2,2-bis[4-(3,4-dicarboxylphenoxy) phenyl] propane dianhydride;4-(2,3-dicarboxylphenoxy)-4′-(3,4-dicarboxylphenoxy)diphenyl-2,2-propane dianhydride;2,2-bis[4-(3,4-dicarboxylphenoxy-3,5-dimethyl)phenyl] propanedianhydride; 2,3,4,5-thiophene tetracarboxylic dianhydride;2,3,5,6-pyrazine tetracarboxylic dianhydride; 1,8,9,10-phenanthrenetetracarboxylic dianhydride; 3,4,9,10-perylene tetracarboxylicdianhydride; 2,2-bis(3,4-dicarboxylphenyl) hexafluoropropanedianhydride; 1,3-bis(3,4-dicarboxylphenyl) hexafluoropropanedianhydride,1,1-bis(3,4-dicarboxylphenyl)-1-phenyl-2,2,2-trifluoroethanedianhydride; 2,2-bis[4-(3,4-dicarboxylphenoxy) phenyl] hexafluoropropanedianhydride; 1,1-bis[4-(3,4-dicarboxylphenoxy)phenyl]-1-phenyl-2,2,2-trifluoro ethane dianhydride; and4,4′-bis[2-(3,4-dicarboxylphenyl)hexafluoroisopropyl] diphenyl etherdianhydride, or a combination thereof, but are not limited thereto. Suchdianhydride compounds may be commercially available or may besynthesized by known methods.

In an embodiment, the tetracarboxylic dianhydride may include3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA),4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), or acombination thereof.

On the other hand, known methods for producing polyamides include alow-temperature solution polymerization method, an interfacialpolymerization method, a melt polymerization method, a solid-phasepolymerization method, and the like. Among them, for example, in thelow-temperature solution polymerization method, carboxylic acid dihalideand diamine may be reacted to form the amide structural unit representedby Chemical Formula 4.

The carboxylic dihalide may be terephthaloyl chloride (TPCl),isophthaloyl chloride (IPCl), biphenyl dicarbonylchloride (BPCl),naphthalene dicarbonylchloride, terphenyl dicarbonylchloride,2-fluoro-terephthaloyl chloride, adipoyl chloride, sebacoyl chloride,and the like, but is not limited thereto.

In an embodiment, the carboxylic dihalide may be terephthaloyl chloride(TPCl).

The diamine for forming the amide structure may be the same diaminecompound as the diamine that is used for forming the imide structure.That is, the amide structure may be formed using at least one of thesame or different diamines used for forming the imide structure.

In an embodiment, the diamine for forming the amide structure along withthe carboxylic dihalide may be 2,2′-bis(trifluoromethyl)benzidine (TFDB)and/or3,3′-bis(1-hydroxy-1-trifluoromethyl-2,2,2-trifluoroethyl)-4,4′-methylenedianiline(MFA-MDA).

The aprotic polar solvent may be, for example, a sulfoxide containingsolvent such as dimethylsulfoxide, diethylsulfoxide, and the like, aformamide containing solvent such as N,N-dimethyl formamide,N,N-diethylformamide, and the like, an acetamide containing solvent suchas N,N-dimethyl acetamide, N,N-diethylacetamide, and the like, apyrrolidone containing solvent such as N-methyl-2-pyrrolidone,N-vinyl-2-pyrrolidone, and the like, a phenol containing solvent such asphenol, o-, m- or p-cresol, xylenol, a halogenated phenol, catechol, andthe like, or hexamethyl phosphoramide, γ-butyrolactone, wherein eachaprotic polar solvent may be used alone or in a mixture thereof.However, the aprotic polar solvent is not limited thereto and anaromatic hydrocarbon such as xylene and toluene may be used.

The amide structural unit and the imide structural unit may be preparedby firstly reacting a diamine and a dicarboxylic dihalide for forming anamide structural unit, and then adding to the same reactor a dianhydridewith or without the further addition of a diamine for forming an imidestructural unit, and thereby a poly(amide-amic acid) copolymer may beprepared.

Alternatively, an amide oligomer having two terminal ends both of whichare terminated with an amino group may be firstly prepared by reacting adiamine and a dicarboxylic dihalide for forming an amide structuralunit, and then the amide oligomer as a diamine monomer may be added toand reacted with a dianhydride to form a poly(amide-amic acid)copolymer. According to the latter method, a precipitation process forremoval of hydrogen chloride (HCl) generated in the amide formingprocess may be omitted, a processing time may be shortened, and a yieldof the poly(amide-imide) copolymer as a final product may be increased.

The amic acid moiety of the polyamic acid or the poly (amic acid-amide)copolymer prepared as described above may undergo a dehydration ringclosure reaction to produce a polyimide or poly (imide-amide) copolymer.A solution including such a polyimide or polyimide-amide copolymer maybe cast on a substrate by a known method, followed by drying and curingthe solution by heating or the like to produce an article such as afilm.

The polyimide-based copolymer solution for forming the opticalenhancement layer 200 is coated on the surface of the film including thepolyimide or poly (imide-amide) copolymer prepared as described above.The method for producing such a polyimide copolymer solution issubstantially the same as the method for producing a polyimide orpoly(imide-amide) copolymer solution for producing the aforementionedlight transmitting substrate 100.

For example, when the optical enhancement layer 200 includes apoly(imide-urethane) copolymer including an imide structural unit and anurethane structural unit, a diol and a diisocyanate compound are firstlypolymerized as monomers for preparing a urethane structural unit, then atetracarboxylic dianhydride and a diamine for forming an imidestructural unit are added to the reactor and polymerized, whereby asolution of a poly(imide-urethane) copolymer including both imidestructural unit and urethane structural unit may be prepared. Thereaction between the diol and the diisocyanate compound to form theurethane structural unit is also well known in this art. There are noparticular limitations for the diol and diisocyanate compound, and anytype of diisocyanate compound may be used as long as the diisocyanatecompound does not significantly adversely affect the optical propertiesand mechanical properties suitable for use as the optical enhancementlayer 200 in the laminated film according to an embodiment. Such dioland diisocyanate compounds may be synthesized by methods known in thisart, or may be commercially available.

When the optical enhancement layer 200 includes an imide structural unitand a siloxane structural unit, tetracarboxylic dianhydride and diaminefor forming the imide structural unit may be mixed and reacted in anorganic solvent, and a siloxane compound including amino groups at bothterminal ends may also be added to the reactor to react as a diaminecomponent to easily prepare a poly(imide-siloxane) copolymer solution.The siloxane compound including amino groups at both terminal ends ispolymerized with the tetracarboxylic dianhydride to form an imidestructural unit, and thus is polymerized with an imide structural unitprepared by a reaction between a diamine compound including no siloxaneand a tetracarboxylic dianhydride to prepare the poly(imide-siloxane)copolymer. The siloxane compounds including amino groups at bothterminal ends may be easily synthesized by methods well known to aperson skilled in this art, or obtained commercially. A person skilledin the art may select the siloxane compound modified with amino groupsat both terminal ends based on the desired mechanical properties andoptical properties. For example, the siloxane compound may berepresented by Chemical Formula 3-1:

In Chemical Formula 3-1,

R^(a) to R^(f), L¹, L², and m are the same as defined in ChemicalFormula 3.

When the optical enhancement layer 200 includes a poly(imide-amide)copolymer including an imide structural unit and an amide structuralunit, it is the same as in the light transmitting substrate 100including the poly (imide-amide) copolymer and thus detailed descriptionthereof will be omitted.

The solutions of the poly(imide-urethane) copolymer, thepoly(imide-siloxane) copolymer, or the poly(imide-amide) copolymerprepared as described above may be further diluted with a solvent or thelike, and may be coated on the film surface of the light transmittingsubstrate 100 including the poly(amide-imide) copolymer and dried,whereby an optical enhancement layer 200 of the laminated film accordingto an embodiment may be easily formed.

The method of preparing the solution for forming the hard coat layer 300is not particularly limited, and the solution may be provided bypreparing a polymer solution that may be used as a hard coatingmaterial, using a method well known to those skilled in the art or byusing commercially available materials. For example, when the hard coatlayer 300 includes a siloxane-containing polymer, a silane compound issubjected to a polycondensation reaction in a solvent to prepare apolysiloxane, and a solution including the polysiloxane obtainedtherefrom may be used as a hard coating solution. Alternatively, whenthe hard coat layer 300 includes an acrylate-containing polymer, acommercially available acrylate polymer may be dissolved in anappropriate solvent, or acrylate monomers may be polymerized to preparean acrylate-containing polymer solution. All of these methods are wellknown to a person skilled in this art, so a detailed description thereofis omitted.

The laminated film includes light transmitting substrate 100 includingthe polyimide or poly(imide-amide) copolymer prepared by the abovemethod, optical enhancement layer 200 disposed on one surface of thelight transmitting substrate 100, and hard coating layer 300 disposed onthe optical enhancement layer 200, or disposed on the other surface ofthe light transmitting substrate 100 opposed to the surface on which theoptical enhancement layer 200 is disposed, such that the hard coatinglayer may be disposed facing the optical enhancement layer 200 with thelight transmitting substrate 100 therebetween, wherein the opticalenhancement layer 200 includes a copolymer including a polyimide and therefractive index of the optical enhancement layer 200 is between therefractive index of the light transmitting substrate 100 and therefractive index of the hard coating layer 300 may suppress generationof interfacial reflection and optical interference fringes due to arefractive index difference between the layers, and thereby opticalcharacteristics, color visibility, and appearance quality may beimproved. Accordingly, such a laminated film may be advantageously usedfor a window film of a display device.

Hereinafter, the embodiments will be described in more detail byexamples and comparative examples. The following examples andcomparative examples are for illustrative purposes and the scope of thepresent disclosure is not limited thereto.

EXAMPLES Synthesis Example 1 Preparation of Amide StructuralUnit-Containing Oligomer

According to Reaction Scheme 1, an amide structural unit-containingoligomer which forms an aramid structure having amino groups at bothends by polymerizing TFDB (2,2′-bis(trifluoromethyl)benzidine) and TPCL(terephthaloyl chloride) is prepared.

Particularly, 1 molar equivalent (0.122 mol, 39.2 g) of2,2′-bis(trifluoromethyl)benzidine (TFDB) and 2.8 molar equivalent(0.343 mol, 27.11 g) of pyridine were dissolved in 700 g ofN,N-dimethylacetamide (DMAC) in a round-bottom flask, and then theresidual TFDB was completely dissolved by further adding 50 ml ofdimethyl acetamide. 0.7 molar equivalent (0.086 mol, 17.4 g) ofterephthaloyl chloride (TPCl) was added in four portions and vigorouslystirred for 15 minutes.

The resultant solution is stirred under the nitrogen atmosphere for 2hours, and then added into 7 L of a NaCl solution containing 350 g ofNaCl and stirred for 10 minutes. The solid is filtered and re-suspendedwith 5 L of deionized water and re-filtered twice more. Subsequently,the remained water is removed as much as possible by appropriatelypressing the final filter cake on the filter and dried under a vacuum at90° C. for 48 hours to provide an amide structural unit-containingoligomer indicated as “amide oligomer” in Reaction Scheme 1. The numberaverage molecular weight of the obtained oligomer is about 1,400gram/mole.

Preparation Examples 1 to 4 Preparation of Polyimide-Based CopolymerSolution for Optical Enhancement Layer Preparation Example 1 Preparationof Poly(imide-urethane) Copolymer Solution

2.52 g (0.0279 mol) of butanediol (BD) and 12.4 g (0.0559 mol) ofisophorone diisocyanate (IPDI), and DBTDL (dibutyltin dilaurate) areadded into 250 ml of 4-neck double wall reactor equipped with amechanical agitator and a nitrogen inlet, the temperature is slowlyincreased to 70° C., and the reaction mixture is stirred at 70° C. for 4hours to be reacted. After completing the reaction, the reactor iscooled to 25° C., and 94 g of dimethyl acetamide (DMAc), 8.95 g (0.0279mol) of 2,2′-bis(trifluoromethyl)benzidine (TFDB), 2.46 g (0.0084 mol)of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 8.70 g(0.0196 mol) of 2,2-bis-(3,4-dicarboxyphenyl hexafluoropropanedianhydride) (6FDA) are added and stirred for 24 hours. Then, 2.3 g ofpyridine and 7.9 g of acetic anhydride are added and stirred for 24hours to provide a poly(imide-urethane) copolymer solution having asolid content of 25 wt %.

Preparation Example 2 Preparation of Poly(imide-siloxane) CopolymerSolution

58 g of dimethyl acetamide (DMAc) is added into 250 ml 4-neck doublewall reactor equipped with a mechanical agitator and a nitrogen inlet,and the temperature is set at 25° C., and 5.7 g (0.018 mol) of2,2′-bis(trifluoromethyl)benzidine (TFDB) is added and dissolved, andthen solution is maintained at 25° C. 3.9 g (0.0045 mol) ofpolydimethylsiloxane (DMS-A11, Gelest) capped with aminopropyl groups atthe both ends thereof is dissolved in 26 g of tetrahydrofuran (THF) andthen added to the reactor. Then, 1.97 g (0.0067 mol) of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 6.94 g (0.0156mol) of 2,2-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride(6FDA) are added to the solution and stirred for 48 hours, and then 1.8g of pyridine and 6.8 g of acetic anhydride are added and stirred for 24hours to provide a poly(imide-siloxane) copolymer solution having asolid content of 17 wt %.

Preparation Example 3 Preparation of Poly(imide-amide-siloxane)Copolymer Solution

120 g of dimethyl acetamide (DMAc) is added into a 250 ml 4-neck doublewall reactor equipped with a mechanical agitator and a nitrogen inlet,the temperature is set at 25° C., and 21.36 g (0.015 mol) of the amidestructural unit-containing oligomer obtained from Synthesis Example 1,0.37 g (0.0011 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and0.673 g (0.0027 mol) of 1,3-bis (3-aminopropyl)-tetramethyldisiloxane(DSX) are added and dissolved, and the solution is maintained at 25° C.1.59 g (0.0054 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride(BPDA) and 6 g (0.013 mol) of2,2-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) areadded into the solution and stirred for 48 hours. Then, 1.5 g ofpyridine and 5.83 g of acetic anhydride are added to the solution, andstirred for 24 hours to provide a poly(imide-amide-siloxane) copolymersolution having a solid content of 20 wt %.

Preparation Example 4 Preparation of Poly(imide-amide) CopolymerSolution

120 g of dimethyl acetamide (DMAc) is added to a 250 ml 4-neck doublewall reactor equipped with a mechanical agitator and a nitrogen inlet,the temperature is set at 25° C., and 21.36 g (0.015 mol) of amidestructural unit-containing oligomer obtained from Synthesis Example 1,0.37 g (0.0011 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and8.87 g (0.0167 mol) of 3,3′-Bis(1-hydroxy-1-trifluoromethyl-2,2,2-trifluoroethyl)-4,4′-methylenedianiline(MFA-MDA) are dissolved, and the solution is maintained at 25° C. 1.23 g(0.0042 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and9.28 g (0.021 mol) of 2,2-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride (6FDA) are added into the solution and stirred for 48 hours.Then, 1.98 g of pyridine and 7.68 g of acetic anhydride are added to thesolution and stirred for 24 hours to provide a poly(imide-amide)copolymer solution having a solid content of 20 wt %.

Preparation Example 5 Preparation of Solution for Forming Hard CoatingLayer Preparation Example 5-1 Preparation of Silsesquioxane

20 mL of ethanol (Samchun Chemicals) and 17.5 g of 1 wt %-dilutedtetramethylammonium hydroxide solution (TMAH: Sigma-Aldrich) are addedto a 100 mL double jacket reaction bath and mixed. 26.5 mL of(3-glycidyloxypropyl)trimethoxysilane (Sigma-Aldrich) is added whilemixing them and mixed at a room temperature for 6 hours. Subsequently,the temperature is increased up to 60° C., and 40 mL toluene(Sigma-Aldrich) is added to the mixture and reacted for 6 hours. Uponcompletion of the reaction, the reaction product solution is washed byusing a saturated sodium chloride solution (Samchun Chemicals), and theremaining moisture is removed by using anhydrous sodium sulfate (SamchunChemicals). Subsequently, solvent was removed by using an evaporator(Daihan Scientific Co., Ltd.) and a vacuum oven (Daihan Scientific Co.,Ltd.).

Preparation Example 5-2 Preparation of Silsesquioxane

20 mL of ethanol (Samchun Chemicals) and 17.5 g of 1 wt %-dilutedtetramethylammonium hydroxide (TMAH, Sigma-Aldrich) solution are addedinto 100 mL double jacket reaction bath and mixed. While mixing them,18.2 mL of [8-(Glycidyloxy)-n-octyl]trimethoxysilane (TCI) is addedthereto and mixed at room temperature for 6 hours. Subsequently, thetemperature is increased up to 60° C., and 40 mL of toluene(Sigma-Aldrich) is added to the mixture and mixed for 6 hours. Whencompleting the mixing, the reaction product solution is washed by usinga saturated sodium chloride solution (Samchun Chemicals), and theremaining moisture is removed by using anhydrous sodium sulfate (SamchunChemicals). The solvent was removed by using an evaporator (DaihanScientific Co., Ltd.) and a vacuum oven (Daihan Scientific Co., Ltd.).

Preparation Example 5-3 Preparation of Hard Coating Solution

Silsesquioxane obtained from Preparation Example 5-1, silsesquioxaneobtained from Preparation Example 5-2, and a cation polymerizableorganic compound represented by the following Chemical Formula A areadded to methyl isobutyl ketone at a weight ratio of 40:40:20,respectively, and stirred. Herein, the amount (solid content) ofsilsesquioxane obtained from Preparation Example 5-1, silsesquioxaneobtained from Preparation Example 5-2, and a cation polymerizableorganic compound represented by the following Chemical Formula A is 50%based on the total weight of the solution. A cation initiator ofIrgacure 250 (BASF) is added thereto in 2 parts by weight based on 100parts by weight of the solid, and a surface characteristic controllingagent of KY-1203 (Shin-Etsu) is added thereto in 0.1 parts by weightbased on 100 parts by weight of the solid and uniformly mixed to providea hard coating layer-forming solution.

A refractive index of the hard coating layer made from the hard coatinglayer-forming solution prepared according to Preparation Example 5-3 is1.5. The refractive index is measured by being set to the Gen-Osc modelin a visible region with an Ellipsometer (M-2000, J. A. Woollam), andthe value at a wavelength of 550 nm is measured.

Preparation Example 6 Preparation of Light Transmitting Substrate Film

101.86 ml of dimethyl acetamide (DMAc) is added into 250 ml 4-neckdouble wall reactor equipped with a mechanical agitator and a nitrogeninlet, which is preheated at 30° C., and 12.6 g (0.0155 mol) of amidestructural unit-containing oligomer obtained from Synthesis Example 1 isadded thereto. Until the oligomer is completely dissolved, the solutionis stirred under a nitrogen atmosphere at 30° C. Then 4.1309 g (0.0093mol) of 6FDA and 1.8239 g (0.0062 mol) of BPDA are slowly added thereto.10 ml of DMAc is further added, and the solution is stirred for 48hours, and then 4.75 g of anhydrous acetic acid and 3.68 g of pyridineare added thereto and further stirred for 24 hours to provide apoly(imide-amide) copolymer solution.

The obtained poly(imide-amide) copolymer solution is coated on a glassplate and cast, and dried on a hot plate at 80° C. for one hour toremove a solvent, and then the coated glass plate is placed into an ovenand heated at a heating rate of 3° C. per a minute from room temperatureto 250° C. Subsequently, the glass plate is slowly cooled, and finally,the poly(imide-amide) copolymer film is separated from the glass plateto obtain the poly(imide-amide) copolymer film having a thickness ofabout 50 μm.

A refractive index of the obtained poly(imide-amide) copolymer film is1.68. The refractive index is set to the Gen-Osc model in a visibleregion with an Ellipsometer (M-2000, J. A. Woollam), and the value at awavelength of 550 nm is measured.

Example and Comparative Example: Fabrication of Laminated Film Example 1

The poly(imide-urethane) copolymer solution obtained from PreparationExample 1 is diluted in 10 wt % in methyl isobutyl ketone (MIBK) andbar-coated on the poly(imide-amide) copolymer film obtained fromPreparation Example 6, and then a solvent is removed in a drying oven toprovide a polymer film having a thickness of about 1 μm.

Subsequently, the hard coating layer-forming solution obtained fromPreparation Example 5-3 is bar-coated on the polymer film, and a solventis removed in a drying oven and cured at 380 mJ/cm² using a UV hardeningdevice (LC6B, Fusion UV) to provide a hard coating layer having athickness of 10 μm, so a laminated film is obtained.

In the obtained laminated film, a refractive index of the opticalenhancement layer made from the poly(imide-urethane) copolymer is 1.58.The refractive index is set to the Gen-Osc model in a visible regionwith an Ellipsometer (M-2000, J. A. Woollam), and the value at awavelength of 550 nm is taken.

Example 2

The poly(imide-siloxane) copolymer solution obtained from PreparationExample 2 is diluted in 10 wt % in methyl isobutyl ketone (MIBK) andbar-coated on the poly(imide-amide) copolymer film obtained fromPreparation Example 6, and a solvent is removed in a drying oven toprovide a polymer film having a thickness of about 1 μm.

Subsequently, the hard coating layer-forming solution obtained fromPreparation Example 5-3 is bar-coated on the polymer film, and a solventis removed in a drying oven and cured at 100 to 500 mJ/cm² using a UVhardening device (LC6B, Fusion UV) to provide a hard coating layerhaving a thickness of 10 μm, so a laminated film is obtained.

In the obtained laminated film, a refractive index of the opticalenhancement layer made from the poly(imide-siloxane) copolymer is 1.59.The refractive index is set to the Gen-Osc model in a visible regionwith an Ellipsometer (M-2000, J. A. Woollam), and the value at awavelength of 550 nm is measured.

Example 3

The poly(imide-amide-siloxane) copolymer solution obtained fromPreparation Example 3 is diluted in 10 wt % in methyl isobutyl ketone(MIBK) and bar-coated on a poly(imide-amide) copolymer film obtainedfrom Preparation Example 6, and a solvent is removed in a drying oven toprovide a polymer film having a thickness of about 1 μm.

Subsequently, the hard coating layer-forming solution obtained fromPreparation Example 5-3 is bar-coated on the polymer film, and a solventis removed in a drying oven and cured at 380 mJ/cm² using a UV hardeningdevice (LC6B, Fusion UV) to provide a hard coating layer having athickness of 10 μm, so a laminated film is obtained.

In the obtained laminated film, a refractive index of the opticalenhancement layer made from the poly(imide-amide-siloxane) copolymer is1.59. The refractive index is set to the Gen-Osc model in a visibleregion with an Ellipsometer (M-2000, J. A. Woollam), and the value at awavelength of 550 nm is taken.

Example 4

The poly(imide-amide) copolymer solution obtained from PreparationExample 4 is diluted in 10 wt % in methyl isobutyl ketone (MIBK) andbar-coated on a poly(imide-amide) copolymer film obtained fromPreparation Example 6, and a solvent is removed in a drying oven toprovide a polymer film having a thickness of about 1 μm.

Subsequently, the hard coating layer-forming solution obtained fromPreparation Example 5-3 is bar-coated on the polymer film, and a solventis removed in a drying oven and cured at 380 mJ/cm² using a UV hardeningdevice (LC6B, Fusion UV) to provide a hard coating layer having athickness of 10 μm, so a laminated film is obtained.

In the obtained laminated film, a refractive index of the opticalenhancement layer made from the poly(imide-amide) copolymer is 1.60. Therefractive index is set to the Gen-Osc model in a visible region with anEllipsometer (M-2000, J. A. Woollam), and the value at a wavelength of550 nm is taken.

Example 5

5 parts by weight of trisilanolphenyl polyhedral oligomericsilsesquioxane (tsp-POSS) represented by Chemical Formula 5-1 is addedto the solution including 100 parts by weight of poly(imide-urethane)copolymer prepared by Preparation Example 1, and the resulting solutionis diluted to a concentration of 10 wt % in MIBK, and bar-coated on apoly(imide-amide) copolymer film obtained from Preparation Example 6,and then a solvent is removed in a drying oven to provide a polymer filmhaving a thickness of about 1 μm.

Subsequently, the hard coating layer-forming solution obtained fromPreparation Example 5-3 is bar-coated on the polymer film, and a solventis removed in a drying oven and cured at 380 mJ/cm² using a UV hardeningdevice (LC6B, Fusion UV) to provide a hard coating layer having athickness of 10 μm, so a laminated film is obtained.

In the obtained laminated film, a refractive index of the opticalenhancement layer made from a solution including 5 parts by weight oftsp-POSS based on 100 parts by weight of the poly(imide-urethane)copolymer is 1.55. The refractive index is set to the Gen-Osc model in avisible region with an Ellipsometer (M-2000, J. A. Woollam), and thevalue at a wavelength of 550 nm is measured.

Example 6

The poly(imide-amide) copolymer solution obtained from PreparationExample 1 is diluted in 10 wt % in MIBK and bar-coated on apoly(imide-amide) copolymer film obtained from Preparation Example 6,and a solvent is removed in a drying oven to provide a polymer filmhaving a thickness of about 1 μm.

Subsequently, the hard coating layer-forming solution obtained fromPreparation Example 5-3 is bar-coated on the poly(imide-amide) copolymerfilm obtained from Preparation Example 6 at an opposite position to theside where the polymer film is formed, instead of being coated on thepolymer film having a thickness of about 1 μm, and a solvent is removedin a drying oven and cured at 380 mJ/cm² using a UV hardening device(LC6B, Fusion UV) to provide a hard coating layer having a thickness of10 μm, so a laminated film is obtained.

In other words, in the laminated film obtained from Example 6, unlikethe laminated films according to Examples 1 to 5, a hard coating layer300 is present on the light transmitting substrate 100, and an opticalenhancement layer 200 is present under the light transmitting substrate100.

In the obtained laminated film, a refractive index of the opticalenhancement layer made from the poly(imide-urethane) copolymer is 1.58,as in Example 1.

Comparative Example 1 Fabrication of Laminated Film Having Only HardCoating Layer on Light Transmitting Substrate

The hard coating layer-forming solution obtained from PreparationExample 5-3 is bar-coated on the poly(imide-amide) copolymer filmobtained from Preparation Example 6, and a solvent is removed in adrying oven and cured at 380 mJ/cm² using a UV hardening device (LC6B,Fusion UV) to provide a hard coating layer having a thickness of 10 μm,so a laminated film is obtained.

Comparative Example 2 Production of Laminated Film IncludingCommercially Available Primer Layer Between Light Transmitting Substrateand Hard Coating Layer

A primer composition including a polymethylmethacrylate(PMMA)-containing polymer and having a refractive index of 1.35available from Flucon is bar-coated on the poly(imide-amide) copolymerfilm obtained from Preparation Example 6, and a solvent is removed in adrying oven to provide a polymer film having a thickness of about 1 μm.

Subsequently, the hard coating layer-forming solution obtained fromPreparation Example 5-3 is bar-coated on the polymer film, and a solventis removed in a drying oven and cured at 380 mJ/cm² using a UV hardeningdevice (LC6B, Fusion UV) to provide a hard coating layer having athickness of 10 μm, so a laminated film is obtained.

Evaluation: Evaluation of Optical Properties and Rainbow Mura Presence

The laminated films obtained from Examples 1 to 6 and ComparativeExamples 1 and 2 are evaluated for optical properties and rainbow murapresence, and the results are shown in the following Tables 1 and 2.Specifically, for the optical properties of the film, a transmittance, ayellowness index (YI), and haze are measured, and the rainbow mura isobserved by the naked eye, and each of them is measured by the followingmethod.

(1) Yellow index (YI) and transmittance (Tr (%), transmittance in arange of 350 nm to 750 nm) are measured with reference to a film havinga thickness of about 60 μm using a spectrophotometer manufactured byMinolta, CM-3600d, and the results are obtained according to ASTM D1925.

(2) The haze is measured using a spectrophotometer manufactured byMinolta, CM-3600d, and the results are obtained according to ASTMD1003-97.

(3) Measurement method of Rainbow Mura: in order to prevent a sidereflection of the laminated film, the surface opposite to the hardcoating layer of the laminated film is bonded with a black acryl plateusing 50 μm PSA manufactured by 3M, and then the mura degree isevaluated as “strong”, “weak,” and “no (none)” by observing the hardcoating layer surface of the laminated film by naked eyes under a threewave lamp. In addition, an image of the three wave lamp reflected on thehard coating layer surface is taken, and the results are shown in FIGS.9 and 10.

Meanwhile, as a control group, only the poly(imide-amide) copolymer filmobtained from Preparation Example 6 is measured for a mura degree, atransmittance, YI, and haze, and the results are shown in FIG. 9.

As shown in FIGS. 9 and 10, the laminated films according to Examples 1to 6 show weak rainbow mura, but the laminated films according toComparative Examples 1 and 2 show strong rainbow mura. On the otherhand, in the case of Control in which only poly(imide-amide) copolymerfilm is present without forming a hard coating layer, rainbow mura isnever shown.

The laminated films according to Examples 1 to 6 show very weak rainbowmura when observed by the naked eye, but show a transmittance of greaterthan or equal to 90% which is higher than in the films according toComparative Examples 1 and 2 and the Control. In addition, theyellowness indexes of the laminated films according to Examples 1 to 6are also lower than films of Control and Comparative Example 1 includingno additional layer between the hard coating layer and thepoly(imide-amide) copolymer substrate. When the commercially availableprimer layer is interposed between the hard coating layer and thepoly(imide-amide) copolymer according to Comparative Example 2, YI is2.3 which is relatively low, and the haze is 0.8 which is also low.Comparative Example 2 shows strong rainbow mura and unfavorable colorvisibility.

The laminated films according to Examples 1 and 6 include the samepoly(imide-amide) copolymer substrate, the same hard coating layer, andthe same composition optical enhancement layer, but the position of theoptical enhancement layer 200 is different. In all cases of the filmsaccording to Examples 1 to 5, the poly(imide-amide) copolymer substratefilm (light transmitting substrate 100), the optical enhancement layer200, and the hard coating layer 300 are orderly laminated, but in thecase of Example 6, the optical enhancement layer 200 is disposed on theopposite surface to the hard coating layer 300 leaving a center of thesubstrate film 100, instead of being interposed between thepoly(imide-amide) copolymer substrate film 100 and the hard coatinglayer 300. Examples 1 to 6 show weak rainbow mura and excellent opticalproperties. Particularly, as in Example 6, the laminated film in whichthe optical enhancement layer 200 is present in an opposite side to thehard coating layer 300 has optical properties superior to the opticalproperties of the laminated film in which the optical enhancement layer200 is present between the poly(imide-amide) copolymer substrate film100 and the hard coating layer 300 as in Example 1.

As shown in the Examples and Comparative Examples, in the laminated filmincluding the poly(imide-amide) copolymer substrate film 100 and thehard coating layer 300, when an optical enhancement layer 200 includinga polyimide-based copolymer is disposed between the two layers or isdisposed on an opposite side to the hard coating layer 300 leaving acenter of the poly(imide-amide) copolymer substrate film 100, it mayreduce an interfacial reflection and a photo interference bycompensating for a refractive index difference between thepoly(imide-amide) copolymer substrate film 100 and the hard coatinglayer 300 to suppress a mura appearance, resulting in a laminated filmthat has excellent color visibility and excellent appearance quality.The laminated film may be usably employed as a window film of thedisplay device required to have an excellent appearance quality.

While this disclosure has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A laminated film comprising a light transmittingsubstrate; a hard coating layer; and an optical enhancement layerdisposed between the light transmitting substrate and the hard coatinglayer or at a position facing the hard coating layer with the lighttransmitting substrate therebetween, wherein the light transmittingsubstrate comprises a polyimide, a poly(amide-imide) copolymer, or acombination thereof, and the optical enhancement layer comprises acopolymer comprising a polyimide.
 2. The laminated film of claim 1,wherein a refractive index of the optical enhancement layer has a valuebetween a refractive index of the light transmitting substrate and arefractive index of the hard coating layer.
 3. The laminated film ofclaim 1, wherein the optical enhancement layer has a refractive index ofabout 1.5 to about 1.7.
 4. The laminated film of claim 1, wherein thecopolymer comprising the polyimide of the optical enhancement layercomprises (a) an imide structural unit, and (b) a urethane structuralunit, a siloxane structural unit, an amide structural unit, or acombination thereof.
 5. The laminated film of claim 4, wherein the imidestructural unit is represented by Chemical Formula 1:

wherein, in Chemical Formula 1, D is a substituted or unsubstitutedquadrivalent C4 to C30 alicyclic organic group, a substituted orunsubstituted quadrivalent C6 to C30 aromatic organic group, or asubstituted or unsubstituted quadrivalent C4 to C30 heteroaromaticorganic group, or a combination thereof, and the alicyclic organicgroup, the aromatic organic group, the heteroaromatic organic group, orthe combination thereof is a single ring, a condensed ring in which atleast two rings are fused, or a ring system comprising at least tworings of the single ring and the condensed ring, wherein the at leasttwo rings are linked by a single bond, a fluorenylene group, —O—, —S—,—C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—,—C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.
 6. Thelaminated film of claim 4, wherein the urethane structural unit isrepresented by Chemical Formula 2:*—(—Y—NH—CO—O—Z—)—*   (Chemical Formula 2) wherein, in Chemical Formula2, Y and Z are each independently a substituted or unsubstituteddivalent C1 to C30 aliphatic organic group, a substituted orunsubstituted divalent C3 to C30 alicyclic organic group, a substitutedor unsubstituted C6 to C30 aromatic organic group, or a substituted orunsubstituted C2 to C30 heteroaromatic organic group, or a combinationthereof, and the alicyclic organic group, the aromatic organic group,the heteroaromatic organic group, or the combination thereof may be asingle ring, a condensed ring in which at least two rings are fused, ora ring system comprising at least two rings of the single ring and thecondensed ring, wherein the at least two rings are linked by a singlebond, a fluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)₂—,—Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—,—C(C_(n)F_(2n+1))₂—, —(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.
 7. Thelaminated film of claim 4, wherein the siloxane structural unit isrepresented by Chemical Formula 3:

wherein, in Chemical Formula 3, R^(a) to R^(f) are each independently asubstituted or unsubstituted C1 to C30 alkyl group, a substituted orunsubstituted C2 to C30 alkenyl group, a substituted or unsubstituted C2to C30 alkynyl group, a substituted or unsubstituted C1 to C30 alkoxygroup, a substituted or unsubstituted C3 to C30 cycloalkyl group, asubstituted or unsubstituted C6 to C30 aryl group, an epoxide-containinggroup, or a combination thereof, L¹ and L² are each independently asingle bond, —O—, a substituted or unsubstituted C1 to C30 alkylenegroup, a substituted or unsubstituted C1 to C30 heteroalkylene group, asubstituted or unsubstituted C2 to C30 alkenylene group, a substitutedor unsubstituted C3 to C30 cycloalkylene group, a substituted orunsubstituted C2 to C30 heterocycloalkylene group, a substituted orunsubstituted C6 to C30 arylene group, a substituted or unsubstituted C2to C30 heteroarylene group, or a combination thereof, and m is aninteger from 0 to
 150. 8. The laminated film of claim 4, wherein theamide structural unit is represented by Chemical Formula 4:

wherein, in Chemical Formula 4, A, E¹, and E² are each independently asubstituted or unsubstituted divalent C1 to C30 aliphatic organic group,a substituted or unsubstituted divalent C3 to C30 alicyclic organicgroup, a substituted or unsubstituted divalent C6 to C30 aromaticorganic group, a substituted or unsubstituted divalent C2 to C30heteroaromatic organic group, or a combination thereof, and thealicyclic organic group, aromatic organic group, heteroaromatic organicgroup, or the combination thereof is a single ring, a condensed ring inwhich at least two rings are fused, or a ring system comprising at leasttwo rings of the single ring and the condensed ring, wherein the atleast two rings are linked by a single bond, a fluorenylene group, —O—,—S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—,—C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.
 9. Thelaminated film of claim 1, wherein the optical enhancement layer furthercomprises a partially condensed polyhedral oligomer silsesquioxanecomprising a functional group capable of forming a hydrogen bond at abroken site of at least one —Si—O—Si— bond.
 10. The laminated film ofclaim 9, wherein the partially condensed polyhedral oligomersilsesquioxane is represented by Chemical Formula 5 or Chemical Formula6:

wherein, in Chemical Formula 5 and Chemical Formula 6, R is eachindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C3 to C30 cycloalkyl group, a substitutedor unsubstituted C6 to C30 aryl group, or a combination thereof, and R′is each independently —OH, —SH, or —NH₂.
 11. The laminated film of claim9, wherein the partially condensed polyhedral oligomer silsesquioxane ispresent in an amount of less than or equal to about 20 parts by massbased on 100 parts by mass of the copolymer comprising the polyimide inthe optical enhancement layer.
 12. The laminated film of claim 1,wherein the hard coating layer comprises an acrylate-containing polymer,a urethane-containing polymer, an epoxy-containing polymer, asilicon-containing polymer, a polycaprolactone, a urethane-acrylatecopolymer, polyrotaxane, a silica-containing inorganic hard coatingmaterial, or a combination thereof.
 13. The laminated film of claim 12,wherein the hard coating layer comprises a silicon-containing polymer,and the silicon-containing polymer comprises an organopolysiloxane. 14.The laminated film of claim 1, wherein the light transmitting substratecomprises a polyimide comprising an imide structural unit represented byChemical Formula 1, or a poly(amide-imide) copolymer comprising an imidestructural unit represented by Chemical Formula 1, an amide structuralunit represented by Chemical Formula 4, or a combination thereof:

wherein, in Chemical Formula 1, D is a substituted or unsubstitutedquadrivalent C4 to C30 alicyclic organic group, a substituted orunsubstituted quadrivalent C6 to C30 aromatic organic group, or asubstituted or unsubstituted quadrivalent C4 to C30 heteroaromaticorganic group, or a combination thereof, and the alicyclic organicgroup, the aromatic organic group, the heteroaromatic organic group, orthe combination thereof is a single ring, a condensed ring in which atleast two rings are fused, or a ring system comprising at least tworings of the single ring and the condensed ring, wherein the at leasttwo rings are linked by a single bond, a fluorenylene group, —O—, —S—,—C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—,—C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof;

wherein, in Chemical Formula 4, A, E¹, and E² are each independently asubstituted or unsubstituted divalent C1 to C30 aliphatic organic group,a substituted or unsubstituted divalent C3 to C30 alicyclic organicgroup, a substituted or unsubstituted divalent C6 to C30 aromaticorganic group, a substituted or unsubstituted divalent C2 to C30heteroaromatic organic group, or a combination thereof, and thealicyclic organic group, aromatic organic group, heteroaromatic organicgroup, or the combination thereof is a single ring, a condensed ring inwhich at least two rings are fused, or a ring system comprising at leasttwo rings of the single ring and the condensed ring, wherein the atleast two rings are linked by a single bond, a fluorenylene group, —O—,—S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—,—C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)—C(C_(n)H_(2n+1))₂—(CH₂)_(q)—,—(CH₂)_(p)—C(C_(n)F_(2n+1))₂—(CH₂)_(q)— (wherein 1≤n≤10, 1≤p≤10 and1≤q≤10), —C(CF₃)(C₆H₅)—, —C(═O)NH—, or a combination thereof.
 15. Thelaminated film of claim 1, wherein the light transmitting substrate hasa thickness of about 30 μm to about 300 μm, the hard coating layer has athickness of about 1 μm to about 30 μm, and the optical enhancementlayer has a thickness of about 0.1 μm to about 10 μm.
 16. The laminatedfilm of claim 1, wherein the laminated film has a transmittance ofgreater than or equal to about 90%.
 17. The laminated film of claim 1,wherein the laminated film has a yellowness index of less than about 3.18. The laminated film of claim 1, wherein the laminated film has a hazeof less than or equal to about
 2. 19. The laminated film of claim 1,wherein when a reflectance of the laminated film is measured at anincident angle of 45 degrees after attaching the laminated film to ablack reflector, an average amplitude of the laminated film in a visiblelight region is less than or equal to about 0.1%.
 20. A display devicecomprising the laminated film of claim 1.